ISSN:0144-557X    

DOI:10.1039/AP98926FX001

出版商:RSC    

年代:1989

数据来源: RSC

摘要:

2 ANALYTICAL PROCEEDINGS. JANUARY 1989, VOL 26 Research and Development Topics in Analytical Chemistry The following are summaries of seventeen of the papers presented at a Meeting of the Analytical Division held on July 18th-I 9th, 1988, in the Polytechnic, Plymouth. Summaries of a further sixteen papers will appear in the February issue. Lithium Ion-selective Electrodes: Optimisation Studies for Blood Serum Analysis C. W. Beswick, G. J. Moody and J. D. R. Thomas School of Chemistry and Applied Chemistry, University of Wales College of Cardiff, P.O. Box 972, Cardiff CF7 3TB Lithium therapy is the most widely used treatment for the control of recurrent depression or manic depression. The safe conduct of such therapy involves the measurement of serum lithium levels which should be maintained between 0.5 and 1 .O mM.At about 2.0-2.5 mM. adverse side-effects appear and higher levels are fatal.' Hence its facile assay in blood samples from patients prescribed lithium salts is clinically desirable. A clinical lithium analyser based on ion-selective electrodes (ISEs) is available for potentiometric analysis,* but there is much room available for improvement. ISE measurements under appropriate conditions have the advantages of compact- ness, low sample minimal operating volume consumption, rapG analysis' and costs. UNQ A Sodium is the main ionic interferent in blood fluid assays, its concentration being about 1400 times higher than the lowest level of 0.1 mM lithium. In the first instance the ISE should be capable of measuring 0.1 mM lithium in the presence of about 150 mM sodium.Other parameters, particularly interference from organic serum components, constitute further problems in the realisation of a suitable lithium ISE. Lithium ISEs have been designed with sensor membranes of diverse materials, but the most encouraging results have been reported for electrodes with sensor membranes consisting of neutral carrier molecules,' admixed with compatible solvent mediators in poly(viny1 chloride) (PVC) matrices. Two broad groups of neutral carrier ionophores are recognised. namely. O D C H 0 0 0 0 OH HO O C H Y X 0 0 U C x: D Fig. 1. University of Sheffield; D = a gift (ETH 2137) from Professor W. Simon, Zurich. Switperland Formulae of lithium sensors studied. A = a gift from Beckman RTIC. High Wycombe.Bucks.: B and C = gifts from Dr. J . F. Stoddart,ANALYTICAL PROCEEDINGS. JANUARY 1989. VOL 26 3 cyclic (crown ethers) and acyclic (lipophilic diamides). However, a third class of ionophores. based on poly- propoxylate adducts,J should also be mentioned. In this study, five different sensor cocktails [A-D in Fig. 1 and a sensor E based on the tetraphenylboratej of a barium propoxylate (PPG 1025)] are described, each having previously been optimised with respect to solvent mediator (Table 1). Table 1. Membrane compositions for lithium ISEs Composition. 'Yo Solvent Sensor mediator* Sensor Mediator PVC A . . . . 2-NPOE 1 .o 66.0 33.0 B . . . . DOPP 1 .o 66.0 33.0 C . . . . DOPP 1 .o 66.0 33.0 D . . . . BBPA 2.0 65.6 32.4 E t . . . . DOPP 1 .o 66.0 33.0 * NPOE = 2-nitrophenyl octyl ether; DOPP = dioctyl phenylphosphonate: BBPA = his( 1-buty1pentyl)adipate; and TPB = tetraphenylborate.+ E = Ba (PPG 1025),,,,, TPB,. Elect rode Opt imisat ion Lithium calibrations performed in aqueous solutions of lithium chloride (Fig. 2) show that each electrode has a nearly Nernstian slope. Sensor D has the best detection limit and, therefore, seems to be the best lithium sensor. However. the 0 > E > 2 -100 0, Q, 0 - - - 200 -6 - 4 -2 Log(lLi+l/M) Fig. 2. standards Calibration of lithium ISEs using aqueous lithium chloride selectivity coefficients, kE.b, show sensor A to be the most selective towards lithium over sodium, although this still does not meet the ideal value required, namely, log(kK.h,) = -3 (Fig. 3). r 1 0 .-1 ' -m 0 2 W -2 ' m -I -3 - 4 I I 1 I Li Na K Mg Ca Pictorial representation of selectivity coefficients. keyg B Fig. 3. The same sensors examined using lithium calibrations in a fixed background of 140 mM sodium chloride (Fig. 4) confirm that sensor A has the best selectivity towards lithium over sodium. This superior selectivity is further emphasised in a + 40 1 0 > E E oi 5 -80 u -40 - -120 -7 -6 -5 - 4 - 3 -2 - 1 Log([ Li + ]/M) Lithium ISE calibration using lithium chloride standards in a Fig. 4. background of 140 mM sodium chloride direct comparison between A and D over the required lithium concentration range of 0.7-1.5 mM as described by Metzger er al.5 Fig. 5 indicates that over this range electrode A shows a difference of 12.5 mM compared with only 6.5 mV for D.Sensor A was, therefore, chosen as the optimum system. - 4 -3 - 2 Log([Li-];~) Fig. 5. Lithium ISE calibration using lithium chloride standards over the clinical range in 140 mM sodium chloride 2 rnM Fig. 6. FIA recording of lithium ISE (electrode A ) response for lithium standards in artificial serum A injected into a carrier stream of artificial herum A4 ANALYTICAL PROCEEDINGS. JANUARY 1989. VOL 26 Studies on Serum by Flow Injection Analysis The sensor cocktail A was incorporated into a flow injection analysis system (a gift from Professor A. A. S. C. Machado, Oporto, Portugal) as described by Alegret et al.6 The carrier solution used was an artificial electrolyte, serum A, as described by Gadzekpo et al.7 The system gave reproducible data (Fig.6) and pH interference studies on a 1 mM lithium standard indicated no interference between pH 5.5 and 9 (Fig. 7). 111111 - 2 4 6 8 10 12 I1 2 60 L Y 3 20 a . . I l l I I II I , I 10min I I I I I I I I I Fig. 7. by FIA pH interference profile of lithium ISE (electrode A) obtained The analysis of serum samples from patients on lithium therapy (Fig. 8) gave reproducible sample peaks, and there was no fouling of the electrode. However, certain samples showed negative peaks, probably because of the low sodium concentra- tion as previously observed by Gadzekpo er d . 7 The data for 1.55 mM A I l l 0.9 mM 0.2 mM I 0.7 mM Fig. 8. Serum analysis by FIA using electrode A with 200 mm7 of samples injected into a carrier stream of artificial serum A interspersed by standards containing 0.5 mM lithium chloride positive FIA lithium peaks were correlated for ISE and the flame photometric data (Fig. 9).Neglecting the outlier in the square box. the relationship was LilsE = 0.81Lin,,,, - 0.09. with a correlation of 0.984. This compares favourably with previously reported results. Conclusions From this study, diamide sensor A appears to be the optimum on the basis of its selectivity towards lithium. However, the study has demonstrated that there are still problems that need 1.2 1 .o 0.8 E . 0.6 - 0.4 0.2 - t .- -1 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 [Li * 1flarne’m~ Fig. 9. Correlation plot of data obtained with lithium ISE (electrode A) by FIA for serum samples neglecting samples showing negative peaks attributable to the level of low sodium content.Equation for full line taking in all points: [LiIISE = 0.81[Lijndmc - 0.11 (correlation 0.952) Equation for dotted line, neglecting outlying square box point: [Li],,, = 0.81[Li]fl,,c - 0.09 (correlation 0.983) to be solved in lithium determinations using ISEs. e.g., insufficient selectivity over sodium, the effect of biochemical serum components on the electrode, the effect of varying electrolyte levels in serum samples and the effect of sample storage .H The Science and Engineering Research Council is thanked for financial support, including a studentship (to C. W. B.). Professor A. A. S. C. Machado. University of Oporto, Portugal, is thanked for helpful discussions, made possible by NATO travel grant (0069184). Finally. Dr. K. Davies of the University Hospital of Wales.Cardiff, is thanked for providing serum samples. References 1. Johnson. F. N.. Editor. ”Depression and Mania: Modern 2. 3. 3. 5 . 6 . 7. 8. Lithium Therapy,” IRL Press. 1987. McCurdy. W . . Chi. Chem.. 1988. 34. 367. Gadzekpo. V. P. Y . , Moody. G. J . , Thomas. J . D. R.. and Christian. G. D.. ton-Selectii~e Elecrrode Re\$.. 1986. 8. 173. Gadzekpo. V. P. Y . , Moody. G. J . . and Thomas. J . D. R.. Analyst, 1985, 110, 1381. Metzger. E . . Dohner. R.. and Simon. W.. A d . C’hrnz.. 1987. 59, 160& 1603. Alegret. S . , Alonso. J . , Bartroli. J.. Lima. J . L. F. C.. Machado. A. A. S. C.. and Paulis. J . M.. Anal. Leu., 1985, 18. 2291. Gadzekpo, V. P. Y . . Moody. G. J.. and Thomas. J . D. R.. Analysl. 1986. 111. 567. Mulryan. G . . Brazil.N . . Day-Cody. D.. and McKeon. P.. Clin. Chern.. 1987. 33. 1943. Development of a Flow Injection Manifold for the Extraction of the Perchlorate Ion with Brilliant Green D. Thorburn Burns, N. Chimpalee and M. Harriott Department of Analytical Chemistry, The Queen’s University of Belfast, Belfast BT9 5AG A flow injection manifold (Fig. 1) has been developed for the the design of Townshend and Alwehaid.3 The optimum spectrophotometric determination of perchlorate as Brilliant reagent and flow conditions are given in Table 1. The Green perchlorate at 640 nm based on an earlier manual interferences are similar to those for the manual procedures’; solvent extraction procedure’.’ and a membrane separator of the principal effects due to chlorate. nitrate. bromide, iodideANALYTICAL PROCEEDINGS, JANUARY 1989.VOL 26 1 2 3 5 - and thiocyanate can be removed by evaporation of samples with concentrated hydrochloric acid. The calibration graph was linear over the range 0-2.5 pg ml-1 of perchlorate and the relative standard deviation for the determination of 1 .O pg ml-1 perchlorate was 1.2% (ten replicates). The procedure has been applied to the determination of perchlorate in reagent and laboratory grades of potassium chlorate. The procedure gave similar accuracy and precision to earlier methods but is more rapid (sampling rate for prepared solutions. 20 h-I); the Table 1. Conditions for the determination of perchlorate ion Mixing coil . . . . . . . . . . Extraction coil . . . . . . . . . . Sampleinjectionvolume . . . . .. Flow-rates: Carrier stream (buffer pH 6) . . . . Reagent stream (Brilliant Green) . . Extraction solvent stream (benzene) . . Organicwastestream . . . . . . Flow-through cell (30 111) . . . . . . Wavelengthofdetection . . . . . . . . . . . . 2 5 0 ~ 1 20cm x 0.5 rnm i.d. 200crn x 0.5 mm i.d. . . 0.95ml rnin I . . 0.85rnlmin 1 . . 0.65rnl rnin I . . 0.68ml min-1 . . . . 640nrn 10 rnm path length detection limit, 0.036 pg ml-l (three times base-line noise), is superior to that for the only other reported FIA method4 for the perchlorate ion based on the AAS determination of copper after extraction of copper(1) - 6-methylpicolinaldehyde azine into isobutyl methyl ketone. We acknowledge with thanks the Du Pont Science Grant 1987-88 used in support of this work. References 1. 2.3. 4. Fogg. A. G.. Burgess, C.. and Thorburn Burns, D.. Analw. 1971. 96, 854. Thorburn Burns. D.. and Tungkananuruk. N . . Anal. Chm. A m . 1987. 199. 237. Townshend. A.. and Alwehaid. A.. personal communication. Gallego, M.. and Valcarcel. M.. Anal. Chim. A m . 1985. 169. 161. Some Recent Developments in Electrochemical lmmunoassays Eileen Buckley and Malcolm R. Smyth School of Chemical Sciences, NlHE Dublin, Glasnevin, Dublin 9, Ireland William R. Heineman and H. Brian Halsall Department of Chemistry, University of Cincinnati, Cincinnati, OH 45227-01 72, USA Immunoassays exploit the molecular recognition properties of biological systems such as immunoglobulins and enzymes. I An antibody can therefore be used as a selective analytical reagent. allowing detection and quantification of an antigen species.The popularity and feasibility of any immunoassay technique depends on the label used. Until recently. radioimmunoassays (RIA) using radioisotopes as labels have been the most popular and have resulted in the most sensitive assays. However, such labels have been declining in popularity owing to problems associated with waste disposal, licensing of laboratories. training of personnel and the high cost of equipment. Labels currently being investigated and used clinically include enzyme labels. chemiluminescent groups. fluorescent groups. metal atoms, electrochemical labels, etc. In electro- chemical immunoassays. both direct and indirect approaches to labelling are currently being investigated. An indirect method would be based on the labelling of the antigen with a non-electrochemical label.e.g.. an enzyme. and would involve monitoring the conversion of a substrate to product following the reaction of the antigen with its corresponding antibody.' A more direct method would involve labelling the antigen with an electrochemical label. e.g.. a heavy metal ion such as indium- (111). and monitoring the response of that label following interaction with the corresponding antibody.3 Alternative methods have been reported recently based on monitoring the changes in the electrochemical response of an antigen (or antibody) adsorbed or immobilised at a charged surface when the corresponding antibody (or antigen) is introduced into the solution.4 The direct approach to monitoring an antigen - antibody interaction is by no means a new concept.Breyer and Radcliffs studied the interaction of an azoprotein with its antiserum using d.c. polarography. No decrease in peak current was observed for the antigen unless the specific antiserum for the azoprotein was added to the cell. Hertlh has studied the dose-response curves for IgG and anti-IgG. anti-ferritin and S. aureus cells and suggested that the formation of surface antibody - antigen complexes disturbs the electrical double layer resulting in a change in the current. Smyth er 01.7 have used adsorptive stripping voltammetry to study the interaction of mouse IgG with anti-mouse IgG. The protein was adsorbed at a hanging mercury drop electrode in a stirred solution at a slightly positive potential and the potential then scanned in a negative direction.Parameters such as accumulation time (la,,), accumulation potential (Ezlc,) and scan rate were optimised and the influence of conditions such as drop size, stirring rate and buffer concentration were also studied. Each protein yielded two faradaic peaks at similar potentials, i.e., at -0.25 and -0.56 V (versus Ag - AgCl). The optimum conditions for the determination of these proteins were: EL,,, +0.05V,r;,,,J00sandscanrate 10mVs-1. Alonger accumulation time gave rise to greater sensitivity but also resulted in a longer analysis time. As increasing amounts of anti-IgG were added to a solution of mouse IgG. the peak currents for mouse IgG decreased in size. If a non-specific antiserum was added, however.no such decrease was ob- served. This is analogous to the behaviour reported by Breyer and Radcliffs for their azoprotein system.6 ANALYTICAL PROCEEDINGS, JANUARY 1989, VOL 26 We have also become interested in learning more about the nature of the electrochemical response of adsorbed proteins, as there is some debate in the literature as to whether this is a faradaic or a non-faradaic process. We have therefore used proteolytic enzymes to produce Fab and F(ab')* fragments of the anti-mouse IgG molecule in an attempt to attribute the observed peaks to a faradaic response (presumably due to reduction of the disulphide link) or a non-faradaic response (such as perturbation of the electrical double layer) or even to a combination of these factors.8 However, this study was inconclusive and there remains some doubt as to the nature of the responses exhibited by proteins at mercury electrodes.9 An example of an indirect electrochemical immunoassay is that developed by Wehmeyer et ,/.,lo which employs an enzyme label.The enzyme is used to catalyse a substrate to product reaction and the latter is detected electrochemically following high-performance liquid chromatography (HPLC) or flow injection analysis (FIA). This technique has been applied to a competitive heterogeneous immunoassay. A new substrate has recently been developed for the above assay. 1 * The conversion of p-aminophenylphosphate (PAPP) to p-aminophenol (PAP) is catalysed by the metalloenzyme alkaline phosphatase (obtained from calf intestine). This conversion of substrate to product has been investigated in a series of different buffer systems and the enzyme activity ( i .e . , substrate to product turnover) was determined in instance. 1.0 - 0.8 - 2 0.6 - F c. C 3 0.4 0 - 0.2 - 0 - each 100 200 300 400 500 Applied potentialimV Fig. 1. buffer (pH 5.0) mobile phase Hydrodynamic voltammogram of PAP in ammonium acetate As both the substrate and product are electroactive, a hydrodynamic voltammogram (Fig. 1) was generated to ascertain the optimum oxidative potential at which to monitor PAP without interference from PAPP (which is also electro- active) and other possible interferents, such as ascorbic acid, that may be present in a biological matrix. The buffer systems studied were tris(hydroxymethy1)aminomethane (THAM), glycine, ammonium hydrogen carbonate, diethanolamine (DEA) and ethylaminoethanol (EAE).The optimum condi- tions for the highest enzyme activity with respect to pH and molarity within each buffer system were determined first and then each buffer system was optimised further to obtain the highest activity between the systems. All enzymic reactions were carried out at a constant temperature of 37°C. After separation by HPLC on a Brownlee C8 reversed-phase column using 0.1 M ammonium acetate buffer (pH 5.0) as eluent. detection of PAP was achieved with a thin-layer electrochem- ical detector. The highest enzyme activity, determined from values of K , and VmaX,, and estimated from direct graphical plots as described by Cornish-Bowden," was exhibited in the EAE ( 0 .1 ~ , pH 9.8) buffer solution. It is anticipated that this enzymic system will give rise to a more sensitive electrochem- ical immunoassay in the future. In conclusion, an examination of the recent literature has revealed that there is increasing interest in the area of electrochemical immunoassays and that there are a wide range of different strategies, both direct and indirect, which are currently (sic) being investigated in this regard. It is anticipated that this area of research in electroanalytical chemistry will continue to blossom in the years to come. 1. 2. 3. 4. 5 . 6. 7. 8. 9. 10. 11. 12. References Kricka. L. J . , in Edmonds. T. E.. Editor. "Chemical Sensors." Blackie, Glasgow and London, 1988, pp. 3-14. Heineman, W. R.. Deutsch, E . , and Halsall. H.B., in Smyth. M. R.. and Vos. J . G.. Editors. "Electrochemistry, Sensors and Analysis," Elsevier, Amsterdam, 1986. pp. 345-353. Doyle, M. J . , Halsall, H. B., and Heineman. W . R.. Anal. Chem., 1982, 54. 2318. Smyth, M. R . , Buckley, E . , Rodriguez Flores. J.. John. R.. and Wallace, G. G., paper presented at "ElectroFinnAnaly- sis." Turku. Finland, June, 1988. Breyer, B., and Radcliff. F. J.. Nature (London). 1951. 167. 79. Hertl, W., Bioelectrochem. Bioenerg.. 1987. 17. 89. Smyth, M. R., Buckley. E.. Rodriguez Flores, J . . and O'Kennedy. R.. Analyst. 1988, 113, 31. Buckley. E., Reilly, P.. Rodriguez Flores, J . , O'Kennedy, R.. and Smyth, M. R., J. Phurm. Biomed. Anal.. submitted for publication. Emons, H.. Werner, G.. and Heineman. W. R.. in prepara- tion. Wehmeyer, K.R., Halsall. H. R.. Heineman. W. R.. Volle. C. P., and Chen, I. W.. Anal. Chem., 1986. 58. 135. Tang, H. T.. Lunte, C. E., Halsall. H. B., and Heineman. W. R.. Anal. Chim. Acta. in the press. Cornish-Bowden, A., "Fundamentals of Enzyme Kinetics." Butterworth, London. 1979. Sampling and Analysis of Organic Vapours in the Flue Gases from Pottery Kilns Naima Bradley and E. David Morgan Department of Chemistry, University of Keele, Staffordshire ST5 5BG The ceramic industry is making increasing use of organic solvents, adhesives, colour and transfer media, particularly in the application of decoration to pottery and china. When the ceramics are fired in the kiln, these materials volatilise or pyrolyse and are emitted in the flue gases at the cooler end of the kiln. In West Germany.' stringent regulations have been laid down for the concentrations of organic substances permitted in the air in workplaces and in flue emissions.Similar controls are likely to be adopted by the EEC and will consequently apply in Britain. An EEC directive has already been published on combating air pollution; it applies to plants engaged in the manufacture of coarse ceramics, refractory bricks, stoneware pipes, facing and floor bricks and roof tiles. In anticipation ofANALYTICAL PROCEEDINGS, JANUARY 1989, VOL 26 7 further legislation designed to control the quality of the environment, we have initiated a project to measure the amount of organic vapour in the flue gases of various types of kilns and for various products of the ceramic industry. Analysis Method In order to determine the very low concentrations of these organic components, it is necessary to undertake a pre- concentration phase.This is carried out by pumping a known volume of the flue gases through a tube filled with an adsorbent. The vapours are then desorbed on heating, separated by gas chromatography and analysed by mass spectrometry. Tenax (surface area about 20 rn' g-1) is a porous polymer based on 2,6-diphenyl-p-phenylene oxide (Fig. 1). Its most important properties are its high temperature stability (350 "C). which allows the elution of many different types of compounds having different relative molecular masses in a relatively short time, and its low affinity for water. r 1 L Fig. 1. Structural model for Tenax Tenax shows selectivity towards certain classes of com- pounds.Hence, polar compounds are more easily retained than non-polar compounds owing to the non-uniformity of its surface charge. Further, high relative molecular mass com- pounds are more easily retained than more volatile com- pounds. Therefore, if Tenax is to be used for quantitative analysis, its limits with respect to its trapping efficiency for the compounds to be sampled need to be established. Breakthrough Volumes A Tenax-filled adsorption tube can be regarded as a very short chromatographic column. The organic contaminants in the air are adsorbed on to the Tenax. travel through it and are eventually purged. A safe sampling or breakthrough volume can be defined as that volume of air containing a particular organic contaminant that can be sampled without a significant amount of contaminant remaining uncollected. The break- through volumes were determined by using the elution analysis technique.2 A gas chromatograph was modified to include a column inlet pressure gauge.A glass column (4 mm i.d.) was packed with 0.35 g of Tenax and connected to a flame ionisation detector. The flow-rate for these measurements was set to between 150 and 200 ml min-1, only half the sampling flow-rate. It has been shown that there is little or no change in the experimentally determined breakthrough volumes for flow-rates of between 100 and 1000 ml min-1 for a similar Tenax adsorption tube.' Breakthrough volumes can vary widely; for example, acetophenone3 has a breakthrough volume of 1258 1 g-1 at 2loC, whereas that of a-pinenej is 4 1 g-1 at 20°C.For this reason the volumes were measured at several higher temperatures and the breakthrough volume at the sampling temperature was obtained by extrapolation. because an approximately linear relationship exists between the logarithm of the breakthrough volume and the increase in the absolute column temperature.s.6 The breakthrough vol- umes for methyl methacrylate and butyl methacrylate were measured at temperatures between 200 and 70°C. At 34°C (maximum sampling temperature) the breakthrough volume for both compounds was found to be greater than 15 1 (the maximum sampling volume used) after extrapolation. Workplace Sampling There are several factors to be taken into account during sampling, such as the temperature of the system, the concen- tration of the contaminants, the flow-rate through the adsorp- tion tube, the sampling volume and, to a lesser degree, the humidity in the air to be sampled.The water content of the air sample is not a significant problem as Tenax is not affected by it. However, such a problem might arise in kilns where combustion gases and gases evolved during the firing process are mixed in the same exhaust pipe. In this instance the humidity can be such that large amounts of water vapour condense inside the Tenax tube and prevent any other compounds from being adsorbed. The optimum flow-rate range is wide for adsorption tubes of this type,h viz., 5-600 ml min-1. In this instance. a flow-rate of 30&400 ml min-1 was chosen because it gave a good compromise between the volume of air sampled and the time required for sampling.The temperature has a marked effect on the breakthrough volume. For methyl methacrylate3 an increase in the tempera- ture from 21.1 to 26.7 "C decreases the breakthrough volume from 144.5 to 95 1 g-1, i . e . , there is a drop in the breakthrough volume of 49.5 1 g-1 for a temperature rise of 5.6"C. Temperatures in kiln exhaust pipes can reach as high as 300 "C. To keep the sampling temperature low. it is therefore advisable to collect the sample as far as possible from the kiln. The adsorption tube is designed so as to minimise the effects of temperature on the Tenax. A glass tube (400 X 4 mm i.d.) is filled with 0.35 g of Tenax (35-60 mesh) held in place by two silanised glass wool plugs.The Tenax-filled portion occupies 130 mm of the adsorption tube. The empty portion is inserted inside the vent and the Tenax filled portion remains outside the kiln vent during sampling and does not come into contact with hot flue gases. Before use, the adsorbent is conditioned under nitrogen at 250°C for 3-6 h to remove all desorbable compounds. 5 2 I I Vent insulation 1;:: gases Fig. 2. Adsorption train. ( 1 ) Adsorption tube; (2) diaphragm pump; (3) digital thermometer; (4) platinum resistance; and ( 5 ) total flow counter The sampling point was selected with the help of the kiln manager and an employee of British Ceramic Research. The equipment that must be transported to the sampling site is shown in Fig. 2. Air is drawn through the adsorption tube ( 1 ) at a rate of 300-600 ml min-I by a diaphragm pump (2).The temperature is recorded with a digital thermometer (3) using a platinum resistance (4) placed inside a glass tube in series with the adsorption tube. The total volume sampled is measured with a total flow counter ( 5 ) . The volume sampled varies between 1 and 15 1 depending on the temperature and the type of substances encountered. After sampling, the tubes are sealed inside a glass container. The duration of the sampling period is 35-45 min. Analysis The organic vapours are desorbed thermally by placing the8 ANALYTICAL PROCEEDINGS. JANUARY 1989. VOL 26 sampling tube (2) (see Fig. 3) inside a tubular oven ( l ) , which has a controllable temperature range of 25-350°C. The adsorption tube is heated to 250 “C for 20 min while a stream of helium (15 ml min-1) is passed through it.The desorbed vapours are then concentrated in a glass-lined U-tube (3) cooled with liquid nitrogen in a Dewar flask (4). When all the material has been desorbed from the Tenax to the U-tube, the U-tube trap is flash heated (in less than 10 s) to 250°C by passing a direct current through the metal covering and the plug of organic vapours is swept on to the chromatography column and separated by means of a temperature programme using a Hewlett-Packard 5890 gas chromatograph coupled to a Hewlett-Packard 5970B mass selective detector with an HP 59970C ChemStation. A fused silica capillary column (12 m x 0.2 mm i.d.) coated with HP-1 (a cross-linked methylsilicone gum), 0.33 pm film thickness, is used.For the first 2 min the chromatographic separation is performed at 30 “C; the column temperature is then programmed to 160°C (at 3 “C min-1). On completion of the chromatographic separation, the compounds are identified using mass spectral libraries. I TO GC - MS Fig. 3. (3) glass-lined U-tube; and (4) Dewar flask Desorption apparatus. (1) Tubular oven; (2) sampling tube; Discussion Two types of continuous feed kiln were investigated. The first was an electrically fired kiln where the ware is placed on a moving belt. The ware travels through the kiln where it is fired at 860-900°C. The material given off as the ware is fired is withdrawn by a powerful extractor fan which, as both ends of the kiln are open, also draws air from the surrounding atmosphere, thereby cooling and diluting the flue gases.The temperature at the sampling point was 34 “C and the flow-rate was 0.62 m3 s-1. Two types of decorative process were used for the ware fired in this kiln: transfers and hand decoration. The compounds identified were butyl and methyl methacrylate from the transfers. In this instance the printing is carried out on a film made from poly(buty1 methacrylate) and poly(methy1 methacrylate). These polymers depolymerise when the ware is fired. In hand decoration a mixture of monoterpenes was identified, viz., cx-pinene, camphor, limonene and carene, which arise from the solvent used. The second type of continuous kiln investigated was a twin tunnel gas fired kiln consisting of two long straight tunnels. The combustion chambers are separated from the ware tunnels by refractory walls,’ the heat being transmitted mainly by conduction through the refractory material. The combustion chambers and the ware tunnels have different exhaust systems. The ware is stacked on to cars and pushed through the kiln on a rail system; most of the ware fired in this kiln is decorated with transfers.The two main compounds identified were butyl and methyl methacrylate. These and other substances are present at levels well below the limits permitted by present legislation and do not make a significant contribution to the level of organic contaminants. We thank the Trustees of the Analytical Chemistry Trust Fund of the Royal Society of Chemistry for the award of an SAC Research Studentship.We gratefully acknowledge the help and guidance of Mr. W. H. Holmes, D. L. Salt and E. Davies of the Whitewares Division of British Ceramic Research, Stoke-on-Trent. E. D. M. thanks the SERC for a grant for the purchase of equipment. References 1. “Bundesministerium des Innern. Technische Anleitung zur Reinhaltung der Luft.” Bundesministerium des Innern. Bonn. FRG. August 1974. pp. 1620. Modification 1986. pp. 12-13. Gallant, R. F.. King, J . W . . Levins. P. L.. and Piecewics. J . F.. Eur. Pat. A p p l . . 60017-781054. March 1978. Poole. C. F.. and Schuette. S . A.. ”Contemporary Practice of Chromatography.’’ Elsevier. Amsterdam. 1984. p. 478. Riba. M. L.. Randrianalimanana. E.. Mathieu. J . . andTorres. L., In[. J . Envirori. Anal. Cherii..1985. 19. 133. Tanaka. T., J . Chromcitogr.. 1978, 153. 7. Brown. R. H., and Purnell. C. J . . J . Chromutogr., 1Y79.178.79. Singer. F., and Singer, S. S . . “Industrial Ceramics.” Chapman and Hall. London. 1963. pp. 1002-1012. 2. 3 . 4. 5 . 6. 7. Potentiometric Determination of Sodium and Potassium in Blood Serum: an Assessment of the Use of Bis(crown ether)-based Ion-selective Electrodes G. J. Moody, Bahruddin B. Saad and J. D. R. Thomas School of Chemistry and Applied Chemistry, University of Wales College of Cardiff, P.O. Box 972, Cardiff CF7 3TB Ion-selective electrodes (ISEs) are steadily replacing flame photometry for the determination of sodium and potassium in body fluids. 1-3 Such determinations are normally conducted with the sodium glass membrane electrode and the valinomycin PVC matrix membrane potassium IS€.However. the use of glass membranes poses various difficulties, such as contamina- tion of the glass membrane surface by proteins, high resistance and interferences from hydrogen ions. Further, there is a continuing search for alternative and improved sensors. The observation that potassium forms a 1 : 2 complex with benzo-15-crown-5 has led to the synthesis of bis(crown ethers) where the two monomeric crown units are linked together by a single bridge.j.5 It has been found4 that the co-operative effect of the two crown ether rings in the bis(crown ethers) gives remarkable selectivity for alkali metal ions through the formation of 1 : 1 cation - bis(crown ether) intramolecular sandwich complexes. Therefore.this study concerns optimisa- tion studies on a bis( 12-crown-4) ( I ) and a bis(benzo-15-crown- 5 ) (11) sensor (Fig. 1) with plasticising solvent mediators in PVC, in the presence and absence of an anion excluder. The optimised system has been utilised in the potentiometric sensing of sodium and potassium ions in serum using analateANALYTICAL PROCEEDINGS, JANUARY 1989. VOL 26 9 ~ Table 1 . Some characteristics of sodium bis( 12-crown-4) (sensor I ) electrodes compared with a commercial (EIL) glass membrane sodium electrode Electrode No. 1 3 4 5 6 7 L Solvent Mole mediator KTCIPB BBPA 0 BEHA 0 DOS 0 NPOE 0 NPOE 5 0 (EIL glass membrane elect rode) Slope/ mV decade I 53.0 52.0 60.0 60.8 61 .o 6O. 5 Detect ion limit/ 4.0 1 .8 1.3 6.3 6.0 3.2 10 - '' hl Log k c l , B [separate solution method (10 2 M)] Resist ancei MR B = K B = Li B = C a B = M g 23 - 1.43 Not evaluated owing to 44 -0.81 poor slopes 60 - 1.38 -2.93 -4.06 -3.96 4 - 1.74 -2.40 -3.88 -3.94 0.08 - 1 .x5 - 1.80 -3.68 -3.51 - - 1 .58 - 1.41 -4.17 -4.21 * BBPA = bis( 1-butylpentyl adipate); BEHA = bis(2-ethylhexql) adipate: DOS = dioctyl sebacate; NPOE = 2-nitrophenyl octyl ether addition and flow injection analysis (FIA) techniques. Opt imisa t ion of Electrodes PVC matrix membranes were cast from mixtures of plasticising solvent mediator (360 mg), PVC (170 mg) and sensor (5 mg) and ISEs were assembled according to established proce- dures.6 In some instances, a 50% molar ratio of tetraphenyl- borate anion excluder relative to sensor was also added.The characteristics of the resulting conventional-type electrodes are summarised in Tables 1 and 2.The separate solution method at a 10-2, concentration of cations was used to evaluate the selectivity coefficients. The best sodium bis( 12-crown-4) and potassium bis(benzo- 15-crown-5) ISE membranes contain NPOE and anion excluder (electrodes 5 and 13. Tables 1 and 2). The best sodium bis( 12-crown-4) electrode ( 5 ) is not only superior to the EIL glass membrane electrode (6) with respect to selectivity over physiologically important cations, but also with respect to response times and pH interferences. The best bis(benzo-15- crown-5) electrode (13) has characteristics similar to the valinomycin electrode (13). The electrodes were tested for possible interferences from biochemicals normally present in blood serum.Standard amounts of biochemicals at the upper range (Table 3). e.g., 0.03O/O urea, were dissolved in 5 mM sodium chloride and potassium chloride, respectively, in electrolytes A and B (that is. mock serum A and B as described bclow). and injected into the FIA stream while running a carrier stream of electrolyte A or B, as appropriate. The peak heights corresponding to five injections of each of the same samples containing the same concentration of sodium or potassium (5 mM) with and without biochemicals were compared. The e.m.f. differences ( A E ) are summarised in Table 3. The studies of the interferences of the biochemicals on the sodium bis( 12-crown-4) electrode are inconclusive owing to the presence of sodium (typically 2-6%) in the Sigma formula- tions, but there is negligible interference on the potassium bis( benzo- 15-crown-5) electrode.Serum Measurements For studies relating the serum measurements, all standard sodium and potassium solutions were prepared in mock serum II Fig. 1. a bis( 13-croivn-4): sensor I1 = a his( benzo-15-crown-5) Structures of bis(crown ether) compounds studied. Sensor I = Table 2. Some characteristics of potassium bis(benzo- 15-crown-5) and \ alinomycin potassium electrodes Lop kK:h Slope' Detection (separate solution method ( 1 0 2 M)] Electrode Solvent Mole % mV limit/ Resistance: No. mediator* KTCIPB decade I 10 51 MR B = Na B = Li B = C a B = M g 7 BBPA 8 BEHA 9 DOS 10 NPOE 11 BEHA 12 DOS 13 NPOE 14 NPOE (Valinomqcin) * Abbreviations as in Table 1 .0 0 0 0 50 50 50 0 52.0 60.0 60.5 61 .o 45.5 57.5 59.2 59.6 7.6 7.5 2.5 3.2 3.5 7.5 8.0 _ _ 3.3 34 43 110 5 3 7 1 0 - - - -3.16 -2.72 -3.23 -4.21 -4.18 -2.53 -3.25 -4.20 -4.08 -1 -._ 58 -3.38 -4.00 -4.04 -2.67 - -3.05 - 3 . I6 -3.94 -4.09 -3.08 -3.14 -3.88 -3.92 -3.02 -2.88 -3.80 -3.96 - -10 ANALYTICAL PROCEEDINGS. JANUARY 1989. VOL 26 Table 3. Effect of biochemicals on bis(crown ether) electrodes AE*lmV r = 0.68 Relative molecular Constituent mass Urea . . . . . . 60 Glucose . . . . 180 Albumin . . . . 69000 a-Globulin . . . . 41 OOG54000 (3-Globulin . . . . 5 x 10h-20 x loh y-Globulin . . . . 1.50000 Mixture of the above sixcomponents . . - r = 0.012 Normal range in human plasma (g per 100 cm3) 0.02-0.03 0.06s-0.09 2.8-4.5 0.3-0.6 0.6-1.1 0.7-1.5 ~ Bis( 12C4) Bis( 15CS) (electrode 5 ) (electrode 13) +0.5 (0.02) 0 (0.02) 0 (0.005) 0 (0.004) +9.0 (0.7) -3.0 (0.4) + 10.2 (0.76) 0 (0.006) -0.5 (0.01) 0 ( 0 ) +8.0 ( 1.2) +3.0 (0.8) + 10.0 (1.6) -2.2 (0.05) * A€ = differences in e.m.f.of a 5 mM solution of the primary ions with and without the biochemicals (s.d. in parentheses. 11 = 5 ) . A (consisting of 5 mM KCI + 1 mM CaC12 + 1 mM MgCI? in 0.05 M Trizma base buffer) and B (consisting of 140 mM NaCl + 1 mM CaCI: + 1 mM MgC12 in 0.05 M Trizma base buffer), respectively, with the pH adjusted to 7.5 using concentrated hydrochloric acid. A direct potentiometric approach ( i . e . , without dilution) for the determinations of sodium and potassium levels in serum using the analate addition technique was used.The best sodium bis( 12-crown-4) electrode, namely electrode 5, in conjunction with a reference electrode, was placed in 1 mM sodium chloride (15 cm-7) in electrolyte A, and spiked with undiluted serum (0.15 cm-7). For the potassium determinations in serum, both the valinomycin and bis(benzo-15-crown-5) macro-ISE (elec- trode 13) were immersed in 0.5 mM potassium in electrolyte B (15 cm-') and spiked with serum (0.15 cm-') and the mV differences were noted. The analate addition was based on where A E is the e.m.f. difference on addition of analyte of unknown concentration C., and volume V,, to a standard solution of analyte of concentration and volume Co and Vo, respectively; S is the slope of electrode. A flow-through sandwich potentiometric detector for FIA in which a PVC sensor cocktail was applied on a conductive epoxy support7 was also used for serum analysis.I I I 0 0 I 120 120 130 140 150120 130 140 150 [ N a ] / m ~ flame photometry Fig. 2. Correlation of potentiometric and flame photometric tech- niques for the determination of sodium, using ISEs ( 5 ) of sensor I [bis( 12-crown-4)) in serum using the analate addition: ( a ) direct potentiometry and FIA; ( b ) indirect potentiometry The blood serum measurements were made on samples obtained from the University Hospital of Wales, Cardiff, which were stored at 4 "C. The determinations were carried out on the same day. before which the samples were allowed to reach room temperature over about 1 h. With regard to electrode quality during use and blood serum measurements.the optimised potassium bis( benzo-15-crown- 5) electrode ( 13) possessed over-all characteristics comparable to those of the valinomycin electrode (14). However. its lifetime is inferior to both the bis( 12-crown-4) electrode (5) and valinomycin electrode (14), as the slopes decreased and the resistance increased after 70 exposures to serum in a macro- ISE mode. The bis(12-crown-4) electrode (8). on the other hand, showed no significant differences in slope and resistance until after 89 contact periods in serum and also functioned well 1 month later. The sodium bis( 12-crown-4) electrode ( 5 ) , although superior to an EIL sodium glass electrode (6), as noted above, does not. however, give a good correlation with flame photometry (Fig. As can be seen from Fig.3, there is a more reasonable correlation between the potassium ion levels in serum deter- mined using the bis(crown ether) electrode (13) and flame photometry. The more laborious analate addition technique seems to yield better correlations than the faster FIA method. 2). 5 0' '1 , , , , ( a ) 0 2 3 4 5 6 7 2 3 4 5 6 7 2 3 4 5 6 7 [ K l l m ~ flame photometry Fig. 3. Correlation of potentiometry and flame photometric tech- niques for the determination of potassium in serum using ISEs (13) of sensor I1 [bis(benzo-lS-crown-5)] ( a ) and (14) valinomycin ( h ) . each using analate addition. and FIA method ( c ) using sensor I1 Conclusion The optimisation of bis( 12-crown-4) and bis( benzo- 15-crown- 5) sensors in association with plasticising solvent mediators in PVC showed that the best electrodes were based on NPOE plasticising solvent mediator and a 50% molar ratio of anion excluder relative to sensor.With regard to the use of these electrodes for serum analysis, the bis( benzo- 15-crown-5) potassium electrodes gave better correlations with flame photometry than the bis( 12-crown-4) sodium electrodes for potassium and sodium determinations, respectively. Financial support and leave of absence from the Universiti Sains Malaysia to one of us (B.B.S.) is gratefully acknowl- edged. Also, Dr. Keith Davies, University Hospital of Wales. is thanked for providing serum samples. References 1. Savory, J . , Bertholf. R. L.. Boyd. C. J . . Bruns. D. E.. Filder. R . A , . Lovell. M., Snipe. J. R.. Wills. M. R.. Czaban.J . D..ANALYTICAL PROCEEDINGS. JANUARY 1989. VOL 26 11 Coffe!. K. F.. and O'Connell. K. M.. And. Cliim. A m . 1986. 180. 99. 2. Oesch. U.. Ammann. D.. and Simon. W.. Cliti. Cheni.. 1986. 32. 1448. Kimura. K.. and Shono. T.. And. Cherii. S ) * t i i p . Ser.. 1985. 22. 155. 2 . 6 . 3 . Worth. H. G . J . . Ancily.sr. 1988. 113. 373. 7. 1. Mallinson. P. R.. and Truter. M. R.. J . Clietn. SOC., Perkiri Trrrns. 2, 1973. 1818. Craggs. A . . Moody. G. J.. and Thomas. J . D. R.. J . Chem. Editc.. 1973, 51. 541. Alegret. S.. Alonso. J . . Bartroli. J.. Lima, J . 1. F. C.. Machado. A. A. S. C.. and Paulis. J . M.. Atid. Leu.. 19x5. IS. 2391. Spectrophotometric Determination of Manganese in Steel After Sol id- p hase Extraction of Tri met h y lene bis( trip hen y I p hosp hon i u m ) Permanganate with Microcrystalline Naphthalene D.Thorburn Burns, D. Chimpalee and N. Chimpalee Department of Analytical Chemistry, The Queen's University of Belfast, Belfast BT9 5AG The permanganate ion forms readily liquid - liquid extractable ion pairs with onium cations that can be used in the spectrophotometric determination of manganese. 1 The first solid - liquid extraction of permanganate using microcrystalline naphthalene is now reported. based on an earlier liquid - liquid extraction using the ethylenebis(tripheny1phosphonium) cation.: The interferences and calibration range were found to be similar for both systems. The optimised procedure for the analysis of steel samples is as follows. Procedure for Steel Samples Reagent Solutions Siilphiiric ncid - phosphoric acid solittion Prepare by mixing 150 ml of concentrated sulphuric acid with 150 ml of 85% orthophosphoric acid and carefully adding the mixture to 600 ml of water.diluting to 1 1 with distilled water. Potossiuni periodate solutiori. 5 Yo m/V Prepare by dissolving 25 g of potassium periodate in a mixture of 300 ml of water and 100 ml of concentrated nitric acid, gently warming to aid dissolution, cooling and diluting to 500 ml with distilled water. p H 6 buffer Prepare by mixing 61.5 ml of 0 . 2 ~ disodium hydrogen phosphate with 438.5 ml of 0.2 M sodium dihydrogen phosphate and diluting to 1 1 with distilled water. Procedure For samples containing 0.2-2.0% of manganese, dissolve accurately weighed 0.3-g samples in 35 ml of the sulphuric acid - phosphoric acid mixture in 250-ml conical flasks.Oxidise with concentrated nitric acid (2 ml) and boil to expel nitrous fumes. If any carbides remain. evaporate the solution to fumes and cool. Add 50 ml of water and warm to dissohre the soluble salts. Cool the flask and, if necessary. filter the contents into a 250-ml beaker. Dilute to 70 ml with distilled water and add 10 ml of concentrated nitric acid. Boil the mixture for 2 min, add 10 ml of 5% potassium periodate solution and boil for a further 4 min. Cool. transfer into a 100-ml calibrated flask and dilute to volume with distilled water.3 Place a 3-ml aliquot of this solution in a 50-ml beaker and add 5 ml of 0.5% potassium periodate solution and 5 ml of 10(% ni/V ammonium fluoride solution. Adjust the pH to 6.0 by careful addition of 2~ ammonia solution or 2~ hydrochloric acid with stirring.Transfer the solution to a ground-glass stoppered conical flask and add 5 ml of pH 6 buffer solution and 5 ml of 1 YO m/V trimethylenebis( triphenylphosphonium) bromide solution. Swirl to mix. add 1 ml of 20% naphthalene in acetone solution and shake vigorously for 30 s. Filter the separated pink solid through a sintered-glass filter (porosity No. 3). Wash with water and drain or suck dry. Dissolve the solid in chloroform and dilute to volume in a 10-ml calibrated flask. Remove any residual water by addition of 0.2 g of anhydrous sodium sulphate and cover the flask with aluminium foil to protect the contents from daylight. Measure the absorbance of the final solution at 538 nm immediately if the steel contains large amounts of chromium.In the absence of chromium extracts are stable for at least 2 h . Table 1. Determination of manganese in certified steels Manganese content. "/o mlm BCS steel Found? No. Certified' 1 101 1 0.22 (021-0.23) 0.210 ? 0.01 1 4571 1 0.30 (0.29-0.30) 0.295 * 0.009 485 0.50 (0.49-0.53) 0.490 k 0.030 2561 1 1.02 ( 1.00-1.03) 1 .oo ? 0.03 214'2 1.61 ( 1 .59-1.62) 1.60 ? 0.03 456 0.17 (0.174.18) 0.163 k 0.010 46W 1 0.67 (0.6&0.68) 0.671 ? 0.009 * Certified range in parentheses. + Mean k9S0/' confidence limits f o r five replicates. Prepare a calibration graph over the range &120 ug of manganese using 0.3 g of high-purity iron with aliquots of standard manganese( 11) solution and proceeding as for the steel samples.Results The results (Table 1 ) for the determination of manganese in a range of British Chemical Standard steels were in good agreement with the certificate values. References 1 . 2. 3. Bowd. A. J . . Thorburn Burn\. D.. and Fogg. A. G.. Tularirri. 1969. 16. 719. Thorburn Burns. D.. and Chimpalee. D.. AnfJI. Chirn. Acru. 19x7. 199, 241. Analytical Panel. *'Methods of Chemical Analysis of I r o n and Steel." British Steel Corporation. Shcffield. 197.1. pp. 82-83.12 ANALYTICAL PROCEEDINGS, JANUARY 1989. VOL 26 Studies on Two Epoxyoctacosahydro[ 12]cyclacene Derivatives as Sensor Coatings on Quartz Piezoelectric Crystals for Detecting Aromatic Vapours M. A. F. Elmosalamy, G. J. Moodyand J. D. R. Thomas School of Chemistry and Applied Chemistry, University of Wales College of Cardiff, P.O.Box 972, Cardiff CF7 3TB F. A. Kohnke" and J. F. Stoddart Department of Chemistry, The University, Sheffield S3 7HF Coated piezoelectric quartz crystals have recently been devel- oped'-4 into a sensitive and selective technique for detecting various air and gaseous pollutants. The basis of the method has been ascribed to the relationship between the mass of coating materials deposited on the crystal surface and the change in frequency according to Sauerbrey's basic equationW A F = -2.3 X 10hPAMIA . . . . (1) where A F is the frequency change (Hz), F is the basic frequency (MHz) of the quartz plate, AM is the mass (g) of the deposited material and A is the area (cm') coated. Equation (1) can be simplified to A F = KC .. . . . . * * (2) where C is the concentration (e.g., mg m-3) of sample gas and K is a constant which refers to the basic frequency of the quartz plate, the area coated and a factor to convert the mass (g) of injected gas data.7.x However, the observed decreases in frequency on applying the logarithmic form of equation (2) yield slopes of less than 1 for plots of logAF versiis log C, that is, the sensing ranges extend to greater dilutions than indicated by equation ( l ) . 7 . 8 Nevertheless, the log - log slopes are increased by attentions to the sampling procedure, but they still fall short of 1. The piezoelectric quartz crystal detection method for gases and vapours has been explored for aromatic hydrocarbons. Thus, a mixture of nujol with trans-chlorocarbonyl bis( tri- phenylphosphine)iridium( I) [rrans-IrCl( CO)( PPh3)?] was used as a detector of aromatic hydrocarbons by Karmarker and "Present address: Dipartimento di Chimica Organica e Biologica.Universita di Messina. Salita Sperone. 31. 98166 Messina. Italy. Guilbault.9 This coating was found to be reactive towards aromatic hydrocarbons but not as sensitive towards aliphatic materials. Toluene in ambient air was monitored using a Carbowax 550-coated crystall" installed in a portable device. This coating gave a linear response over a long range with a reproducibility of better than 4%. No interferences were observed from inorganic gases. such as carbon monoxide, 1 2 Fig. 1. tive (1) and tetraepoxy analogue (2) Formulae of hexaepoxyoctacosahydro[ 12lcyclacene deriva- sulphur dioxide, ammonia or nitrogen dioxide, at the level studied.1 0 Organic vapours gave some interference but were insignificant at the 5% VIV level. Carbowax 1000 has been investigated for 2-nitrotoluene. 1 1 Edmonds and West" examined the behaviour of various coatings on a 9-MHz AT-cut quartz crystal towards toluene and chloroform with regard to various parameters and reported that Pluronics 64 (a GLC stationary phase material) is the most sensitive coating for ethylbenzene, 2-methyltoluene and hex- ane. Table 1. Response (AFIHz) of coated quartz crystal to various dilutions of headspace nitrobenzene vapour (sensor 1) AFIHz for nitrobenzene for 2.42 factors of dilution Day 3 7 7 - * * Mean 8 10 15 20 33 25 27 29 32 35 38 58 7 Headspace v a po u r 1 1 1 109 113 111 110 110 90 88 73 80 85 88 81 9( 1 74 70 73 1 x 2.42 59 6( 1 61 60 62 58 52 48 36 43 53 50 46 48 44 40 50 3 x 2.42 38 38 3Y 38 43 31 28 34 '4 25 37 29 37 28 76 '4 35 3 x 2.42 25 '4 26 25 25 20 16 16 19 1Y 20 19 18 18 26 19 -- 97 -- 4 x 2.42 16 16 17 16 17 13 1 1 14 12 12 13 12 13 13 1.3 13 16 5 x 2.43 10 11 9 10 12 10 9 10 10 Y 9 9 8 10 9 9 11ANALYTICAL PROCEEDINGS.JANUARY 1989. VOL 26 13 More recently, in a study of the roles of some chemically modified cyclodextrins. 2.6-per-O-(rerr-butyldimethylsilyl)-~- cyclodextrin (DSKD) was found to be the best sensor for the range from about 80 to about 4 x 105 mg m-3 benzene vapour in air13 with good selectivity, toluene being the most serious interferent .I3 Charcoal, PEG-750. PEG-400 and other materials have been assessed as coatings for the piezoelectric quartz crystal detection of nitrobenzene.IJ The sorbents were tested to fill equilibration for 35 mg m-3 of nitrobenzene.The toxicity of nitrobenzene (the maximum allowable concentration is 5 mg m-3) presents a need for such sensitive detectors. A further prospect for a piezoelectric quartz crystal coating for this purpose is offered by the recently synthesised".lh hexa- epoxyoctacosahydro[ 12lcyclacene derivative (1) which is eval- uated here. Also examined was the tetraepoxy analogue (2) for its prospects as a possible sensor for toluene vapour. The structures of 1 and 2 are shown in Fig. 1. Experimental The apparatus and detector cell used are as described previously.8 measurements being made at 25 ? 0.1 "C.The AT-cut quartz crystal with gold-plated electrodes on each side (Quartz Crystal, Wellington Crescent, New Malden, Surrey, but now available from Webster Electronics, Rosemills. Hartbridge. Ilminster. Somerset) had a resonant frequency of 9 MHz. The synthesis of the epoxyoctacosahydro[ 12lcyclacene derivatives 1 and 2 have been described in detail elsewhere. l i . l h Test Samples Nitrobenzene vapour samples were obtained with a previously flushed out 10-cm3 syringe from the headspace of its liquid equilibrated under dry air in a thermostat at 25°C. The concentration was calculated to be 1.84 x 103 mg m-3 from the quoted17 equilibrium vapour pressure of 0.277 mm Hg. However, there are other vapour pressures in the literature. namely. 0.31018 and 0.246 mm€-lg,l(~ corresponding to 2.24 X 103 and 1.63 x 103 mg m-3 of nitrobenzene.respectively. The samples of toluene and other vapours were obtained similarly. 17-19 Serial dilutions of the headspace samples were prepared by the syringe dilution method.9 modified as described pre- vious1y.X Successive dilutions of samples using air dried over silica gel were delayed by 30-60 s in order to allow the vapour to diffuse throughout the air in the syringe. Ammonia test samples were taken from the headspace of 2~ ammonia solution as previously described.8 Method of Coating Compound 1 or 2, as appropriate. dissolved in chloroform (0.6% mlV), was brush-coated on the surface of the electrode on each side of the crystal. After drying, the coated crystal was fitted into the detector compartment of the apparatus assembly.8 In each instance, the coating applied caused a decrease of ca.12 kHz in the frequency of the crystal. The sensor compounds could be removed from the crystal by stripping with chloroform and air dried ready for reloading. Operation of Piezoelectric Quartz Crystal Detection Apparatus The responses of coated piezoelectric quartz crystals were tested with nitrobenzene ( 5 cm3 injected at the rate of 8 s cm-?) of six different dilutions of the headspace vapour and the mean decrease in frequency for replicate samples ( n = 3) was calculated. All samples were injected into a carrier air stream provided with a Pitman Instruments Model 7069 air sampler pump and dried by passing through silica gel before reaching the quartz crystal cell.The air stream rate was 20 cm3 min-1. A typical recorder trace (Fig. 2) illustrates the response of this detection system which corresponds to a flow injection analysis procedure. Results and Discussion Sensor 1 Calibration data for many nitrobenzene runs with coating of sensor 1 are shown in Table 1 and Fig. 3. The frequency decreases ranged. respectively, from 11 1 Hz for nitrobenzene headspace vapour to 10 Hz for headspace vapour diluted with dry air 5 x 2.42 times (the factor 2.42 allows for the volume of vapour in the needle and connector in addition to 4 cm3 left in the syringe after evacuating 6 cm3 of vapour from the 10-cm3 syringe). Taking account of the headspace vapour containing Table 2. Response of a piezoelectric quartz crystal (gold electrode) to various vapours for coatings of components 1 and 2 Compound 1 Compound 2 : AFiHz.Response. ARHz No. o f calibrations response. Interferent 10T mg m- 1st coating 2nd coating 1st coating Zndcoating 1st coating Concent ration ' 3 3 - 3 - Toluene . . . . . . 30.0 19 '0 6 L 86 6.6 13 13 6 L 1.5 9 10 6 2-Nitrotoluene . . . . 1.40 48 46 6 0.31 25 23 6 - 0.07 16 15 6 - 0.33 10 30 6 0.07 1 0 11 6 2 3.37 1 1 12 6 - 0.74 8 9 6 - 17 18 5 0.02 - 0.30 10 12 5 L 4.2 x 9 6 - 6 7 A 0.9 - Ammonia . . . . . . 3.90 40 42 3 1 0.48 19 19 3 1 0.06 10 1 1 3 1 3 136 7 - ? - 3-Nitrotoluene . . . . 1.50 38 37 6 - 85 ? - - 7 7 - 7 3 3 - 7 - 3 1 7 - Chlorobenzene . . . . 15.4 16 18 6 L 81 - Bromobenzene . . . . 4.18 30 31 5 L 75 Benzene . . . . . . 19.2 10 12 6 - 125 - - - - Nitrobenzene .. . . 1 .84 111 109 3 3 121 Calculated from vapour pressure data. except for ammonia. which was analysed ;is discussed14 ANALYTICAL PROCEEDINGS. JANUARY 1989. VOL 36 about 1.84 x 1 0 3 mg m-3 of nitrobenzene (calculated for 0.277 mmHg vapour pressure), the decreases in frequency are less than the 136, 53. 86 and 48 Hz observed by Sanchez-Pedreno et a1.14 for 35 mg m-3 of nitrobenzene by charcoal, PEG-400, PEG-750 and Quadrol. respectively. However, these other data14 are for full equilibration, whereas the data presented here are for successive injections of samples. t 8993.120 I i C 0) 3 0- L L 2 11 Hz /- 320 Headspace 1 vapour 1840 mg m - 3 J Time - Fig. 2. using a quartz crystal (gold electrode) coated with compound 1 Typical recorder trace of a calibration of' nitrobenzene vapour Clieriiical interferences Nitrobenzene is a toxic substance and the threshold limit value is 5 mg m-3 (corresponding to 10-6 mol mol-1). Therefore, various organic interferences were tested and the data are summarized in Table 2.Except for 2- and 3-nitrotoluene, there were no significant interferences from a wide range of aromatic vapours, namely. toluene. chlorobenzene. bromobenzene and benzene, but ammonia is an interferent. While the concentration range studied by Sanchez-Pedreno et ~ 1 . 1 4 (10-50 mg m-3) was at the lower end of the range for this work, their turn-round time between samples was long. ranging from 10.2 to 29.2 min, according to sorbent. Also, the sorbents used are not selective, so that much of the sensitivity advantage is lost. Lifetime of the detector The coated quartz crystal detector for nitrobenzene functioned for 9 weeks (Fig.3). although the sensitivity (Table 1) declined. During this time, the coated crystal was also exposed on many occasions to seven different interferences but with no lasting deleterious effect (Table 2). After evaluation for nine weeks. the sensor coating was removed with chloroform and fresh hexaepoxyoctacosahydro- [ 12)cyclacene sensor I applied. The newly loaded sensor behaved similarly towards the various compounds previously investigated (Table 2). Sensor 2 Sensor 2 does not show the degree of selectivity shown by sensor 1 towards nitrobenzene towards any of the aromatic vapours studied (Table 2, last column), and ranks as a more universal type of sensor.However. the response towards 2-nitrotoluene equals, and even slightly excels. that towards nitrobenzene. Mode of Detection X-ray crystallography has shownIi.lh that compound 1 supports a rigid cavity wherein the two benzene rings are parallel with an interplanar ring into the cavity such that it assumes an orthogonal relationship with respect to the two benzene rings. Particularly for a phenyl group carrying an electron-with- drawing substituent. the resulting edge-to-face interaction'(c 2i could be sufficiently stabilising electrostatically to allow nitrobenzene to enter the cavity of 1. Equally well. however. the nitrobenzene could be trapped temporarily within inter- stitial space between the doughnut-shaped molecules. Further experimentation in progress will, it is hoped, resolve this dilemma and provide the basis for explaining the relatiire lack of selectivity exhibited by compound 2.2.0 1.6 - N I Li m 1 a - 1.2 0.8 - 2 - 1 0 Log [nitrobenzene] normalised to [headspace] = 1 Fig. 3. Calibration of a piezoelectric quartz crystal coated with compound 1 for S-cm3 samples of nitrobenzene headspace vapour and successive dilutions ( ~ 3 . 4 3 ) thereof. Time: 0.3: A. 15: C. 25: 0. 39: A. 38: and .. 59 d Conclusion Quartz crystals coated with a hexaepoxyoctacosahydro[ 121- cyclacene derivative (1) facilitate the detection of nitrobenzene vapour. Except for ammonia and 2- and 3-nitrotoluene. interference from some common aromatic compounds is minimal, and the device has a long operational lifetime.Coatings of a corresponding tetraepoxy derkrative (2) are of more universal sensing ability. The authors are grateful for the award of a Leverhulme Research Fellowship (to J.F.S.). The joint research pro- gramme was made possible as a result of generous support from the SERC Chemistry Committee under the auspices of their initiative on chemical sensors. Zagazig University. Egypt. is also thanked for leave of absence and financial assistance (to M. A.F.E. ). References 1. 3. 3 . Hlavay. J . . and Guilbault. G . G.. A t i d Climz.. 1977.49. 1890. Guilbault. G. G.. foii-Selecii\x> Electrode Re\. .. 19x0. 2. 3 . Guilbault. G . G.. and Ngeh-Ngwainbi. J . . in Guilbault. G. G.. and Mascini. M.. Editors. "Analytical Uses of Immobilised Biological Compounds for Detection.Medical and Industrial Uses." NATO AS1 Series. Series C : Mathematical and Physical Sciences. Vol. 336. Reidel. Lancaster. 198X. p. 187. Alder. J . F.. and McCallum. J . J . . Atzulj-st. 1983. 108. 1169. Sauerbrey. G. Z.. Z . P l i j ~ . . 1959. 155. 306. Sauerbrey, G. Z . , Z . P1ij.s.. 1964. 178. 457. 4. 5 . 6 .ANALYTICAL PROCEEDINGS, JANUARY 1989. VOL 26 1s 7. 8. 9. 10. 11. 12. 13. 11. 15. 16. Beitnes. H.. and Schrsder. K.. A n d . Chirn. Acrri. 1984. 158. 57. Lai. C. S . - I . . Moody. G. J . . and Thoma\. J . D. R.. A n a l w . 1986. 111. 51 1 . Karmarkar. K. H.. and Guilbault. G . G.. Etzl-iron. Lett.. 1975. 10. 237. Ho. M. H.. Guilbault. G. G.. and Reitz. B.. Anal. Chetn.. 1980. 52. 1489. Tomita. Y.. Ho. M. H.. and Guilbault. G. G.. Anal.Chetn., 1979. 51. 1475. Edmonds. T. E.. and West. T. S . . Anal. Chini. Acra. 1980. 117. 147. Lai. C. S.-I.. Moody. G . J . . Thomas. J . D. R.. Mulligan. D. C., Stoddart. J . F.. and Zarzycki. R.. J . Chem. Soc., Perkiri Trans. 2. 1980. 319. Sanchez-Pedreno. J . A. 0.. Drew. P. K. P.. and Alder, J . F . . Anal. Chim. A m . 1986. 182. 285. Kohnke. F. H.. Slawin. A. M. Z.. Stoddart. J . F.. and Williams. D. J.. Ange14,. Chem.. In[. Ed. Engl.. 1987, 26. 897. Ashton. P. R.. Isaacs, N . S.. Kohnke. F. H.. Slawin, A. M. Z . . Spencer. C. M.. Stoddart. J . F.. and Williams. D. J . , Hrl\j. Chim. Acfa, in preparation. 17. 18. 19. 20. 21. 22. 23. 21. 25. Kirk. R. E . . and Othrner. D. F.. "Encyclopedia of Chemical Technology." Volume 21. Third Edition. Wiley. New York and Chichester, 1983, p.387. West, R. C., and Astle. M. J . , Edirors, "Handbook of Chemistry and Physics," Sixty-fifth Edition. CRC Press, Boca Raton, FL, 1985. pp. D204 and D206. Dean. J . A.. Ediror. "Lange's Handbook of Chemistry." Twelfth Edition, McGraw-Hill. New York. 1979, pp. l(k-52. Gould. R . 0.. Gray. A. M., Taylor. P.. and Walkinshaw. M. D.. 1. Am. Chem. Soc.. 1985. 107, 5921. Burley. S. K.. and Petsko. G. A.. Science. 1985. 229. 2 3 . Burley, S . K . . and Petsko. G . A.. J . Am. Chem. Soc.. 1986. 108. 799s. Slawin. A. M. Z . . Spencer. N.. Stoddart, J . F . . and Williams. D. J . , J . Chem. Soc., Chem. Cornmun.. 1987. 1070. Alston. D. R.. Slawin, A. M. Z . . Stoddart. J . F., Williams. D. J . , and Zarzycki. R., Angerr,. Chern., Inr. Ed. Engl.. 1987.26. 693. Moody, G. J . , Owusu. R. K., Slawin, A. M. Z . . Spencer. N . . Stoddart. J . F.. Thomas. J . D. R.. and Williams, D. J . , Angerr.. Chern., lnt. Ed. Engl.. 1971. 26. 390. Some Analytical Applications of Polymer Modified Electrodes Mary Meaney, Johannes G. Vos and Malcolm R. Smyth School of Chemical Sciences, NlHE Dublin, Glasnevin, Dublin 9, Ireland Gordon G. Wallace Department of Chemistry, University of Wollongong, Wollongong, New South Wales 2500, Australia The design of chemically modified electrodes (CMEs) for electroanalysis has been the subject of much research in the last few years.1-1') In attempts to enhance the sensitivity of voltammetric methods. the use of CMEs has three major advantages. The first is that the coating employed can be used to provide a surface that is capable of efficient pre-concentra- tion.The second advantage can be seen in terms of the facilitation of faster electron transfer reactions and the third in better surface protection, resulting in decreased memory effects. A variety of different approaches to electrode modifi- cation have been reported. One of the first approaches was introduced by Brown er ul. .? whose method involved modification of an electrode surface through the irreversible adsorption of selected aromatic hydrocarbons. Using this approach, Landum er ul. 3 described the electrochemical characteristics of methyl viologen on gold. whereas Davis and Murray4 studied the behaviour of iron porphyrins on Sn02. A second approach has been to modify the electrode surface through the covalent attachment of electroactive groups via silanisation reactions on oxide surfaces.Hence Abruna et ul. have described the use of trichlorosilane for this purpose, whereas Wrighton and co-workers have used trichlorosilyl- ferrocene to modify p1atinum.h gold7 and germanium8 elec- trodes. In our laboratories. the main interest in this area of research has been to investigate the use of polymer modified electrodes for analytical purposes.y-12 The electrodes can be coated either with electrochemically generated polymer layers, such as polypyrrole,Y.l3 or with chemically generated redox polymers. such as those containing ruthenium( 11) - ruthenium(II1) active sites.ll.12.14 The former type of polymer modified electrode has been shown to have the capability to pre-concentrate analytes at the electrode surface, whereas the use of ruthenium- containing polymers has been found to enhance the electron transfer characteristics of some sluggish electrode processes.This enhancement is thought to be due to the electrocatalytic properties of the ruthenium sites in the polymer, through which rapid charge transfer can occur, possibly via a charge hopping Drocess. These redox polymers (dissolved in an appropriate low- boiling organic solvent) are usually applied directly on to the electrode surface using a pipette and the solvent is allowed to evaporate. Other methods of introducing ruthenium on to an electrode surface have been reported based on electrostatic interactions between polyelectrolytes,15 incorporation of ruthenium oxide in polypyrrole,lh formation of a bilayer electrode such as platinum - ruthenium polymer - polypyrrole17 and attachment of ruthenium(I1) to amino functional groups on graphite electrode surfaces.18 In a stationary solution, we have shown that by using an [ Ru( bpy)?( PVP)5Cl]Cl modified electrode (bpy = bipyridyl; PVP = polyvinylpyridine), it is possible to increase the sensitivity in the determination of analytes such as Fell, nitrite and nickel bis(2-hydroxyethy1)dithiocarbamate [Ni(HDTC)?] by a factor of at least two compared with an uncoated glassy carbon electrode.'(' Chemical modification of this kind also resulted in better reproducibility, as no adsorption due to the oxidation of HDTC-, for instance, was apparent. However. the major drawback of using electrocatalytic polymers in this way is that all the analytes give rise to responses that are at and above the level of the background signal owing to the oxidation of Ru" to RuIII.This problem can be overcome if the analysis is carried out in a flowing solution, because if the electrode is held at a fixed potential, the signal due to the Ru" - RuI" couple in the polymer layer then becomes part of the background signal. We have demonstrated using flow injection analysis (FIA) that the use of such a polymer modified electrode (incorporated as the working electrode in an electrochemical detector) can result in a 3-6 fold increase in the peak height for selected metal - HDTC complexes compared with an uncoated glassy carbon electrode. 19 However, problems were encountered due to loss of the polymer layer on continuous use. This loss can be attributed to the fact that the polymer layer is only weakly bound to the surface of the carbon substrate by chemisorption. We have therefore investigated several means of improving the stability of the polymer layer, which have involved treatment with ultraviolet light to induce greater cross-linking of the polymer layer, and formation of bilayer electrodes incorporat-16 ANALYTICAL PROCEEDINGS. JANUARY 1989. VOL 26 ing the ruthenium polymer coated with either a conductive polymer [such as poly(3-methylthiophene)] or a non-conduc- tive polymer [such as poly(N-ethyItyramine)].2(’ These stabil- isation procedures resulted in a slight loss of sensitivity, but produced electrodes that had half-lives more than six times longer than those of the non-stabilised electrodes. It is anticipated that these polymer modified electrodes will eventually find further use in the quantification of inorganic species using FIA and HPLC techniques. 1. 2. 3. 4. 5 . 6. 7. References Wallace. G . G.. in Edrnonds. T. E . , Editor, “Chemical Sensors” Blackie, Glasgow and London, 1988, pp. 132-154. Brown, A. P.. Koval, C.. and Anson. F. C.. J. Electroanal. Chem., 1976. 72. 379. Landum. H . L., Salmon, R. T., and Hawkridge. F. M..J. Am. Chem. Soc.. 1977, 99. 3154. Davis, D. G., and Murray, R. W., Anal. Chem.. 1977.49, 194. Abruna. H. D.. Meyer. T. J.. and Murray, R. W.. Inorg. Chem.. 1970, 18. 3233. Wrighton. M. S . , Austin, R . G., Bocarsly, A. B., Bolks, J . M.. Haas, 0.. Legg, K. D., Nadjo. L.. and Palezzolto, M. C.. J . Electroanal. Chem.. 1978, 87, 429. Wrighton, M. S . . Palezzolto. M. C.. Bocarsly, A. B.. Fischer. A. B.. and Nadjo. L.. J . Am. Chem. SOC.. 1978, 100. 7262. 8. 9. 10. Bolts, J . M., and Wrighton. M. S . , J . Am. Chem. SOC.. 1978. 100. 5257. O’Riordan, D. M. T., and Wallace. G. G., Anal. Chem.. 1986, 58, 128. Irnisides, M. D.. O’Riordan. D. M. T., and Wallace, G. G.. in Smyth, M. R.. and Vos. J. G.. Editors. ”Electrochemistry. Sensors and Analysis.“ Elsevier. Amsterdam, 1986. pp. 293-302. Haas. 0.. and Vos. J . G., J. Electroanal. Chem.. 1980. 113. 139. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. Geraty, S. M.. Arrigan. D. W. M., and Vos. J . G., in Smyth. M. R . , and Vos. J . G.. Editors. “Electrochemistry. Sensors and Analysis,” Elsevier, Amsterdam. 1986, pp. 303-308. Bull, R. A., Fan, F. R.. and Bard. A. J . . J . Electrochem. Soc.. 1982, 129. 1009. Andrieux, C. P., Haas, 0.. and Saveant, J. M., J. Am. Chem. SOC., 1986, 108, 8175. Oyarna, N.. and Anson, F. C.. Anal. Chem., 1980. 52. 1192. Noufi. R., J. Electrochem. SOC.. 1983. 130. 2126. Murao, K.. and Suzuki, K., Polym. Pre.. Am. Chem. SOC. Div. Polym. Chem., 1984, 25. 260. Oyama. N.. Brown, A. P.. and Anson. F. C.. J. Electroanal. Chem., 1978. 87. 435. Barisci. N.. Wilke, E . . Wallace. G. G.. Meaney, M.. Smyth, M. R . . and Vos, J . G.. Elecrroanal~sis, submitted for publication. Meaney. M.. Smyth, M. R.. Vos, J . G.. and Wallace. G. G.. Electroanalysis, in the press.

ISSN:0144-557X    

DOI:10.1039/AP9892600002

出版商:RSC    

年代:1989

数据来源: RSC

摘要:

ANPRDI 26( 1 ) 1-44 (1 989) Proceedings of the Analytical Division of The Royal Society of Chemistry 32 1 Editorial 2 SUMMARIES OF PAPERS 2 Research and Development Topics in Analytical Chemistry 2 4 5 6 8 11 12 15 16 19 20 22 24 27 29 'Lithium Ion-selective Electrodes: Optimisation Studies for Blood Serum Analysis' by C. W. Beswick, G. J. Moody and J. D. R. Thomas 'Development of a Flow Injection Manifold for the Extraction of the Perchlorate Ion with Brilliant Green' by D. Thorburn Burns, N. Chimpalee and M. Harriott 'Some Recent Developments in Electrochemical lmmunoassays' by Eileen Buckley, Malcolm R. Smyth, William R. Heineman and H. Brian Halsall 'Sampling and Analysis of Organic Vapours in the Flue Gases from Pottery Kilns' by Naima Bradley and E.David Morgan 'Potentiometric Determination of Sodium and Potassium in Blood Serum: an Assessment of the Use of Bis(crown ether)-based Ion-selective Electrodes' by G. J. Moody, Bahruddin B. Saad and J. D. R. Thomas 'Spectrophotometric Determination of Manganese in Steel After Solid-phase Extraction of Trimethylenebis(tripheny1phosphonium) Permanganate with Micro- crystalline Naphthalene' by D. Thorburn Burns, D. Chimpalee and N. Chimpalee 'Studies on Two Epoxyoctacosahydro[ 12]cyclacene Derivatives as Sensor Coatings on Quartz Piezoelectric Crystals for Detecting Aromatic Vapours' by M. A. F. Elmosalamy, G. J. Moody, J. D. R. Thomas, F. A. Kohnke and J. F. Stoddart 'Some Analytical Applications of Polymer Modified Electrodes' by Mary Meaney, Johannes G.Vos, Malcolm R. Smyth and Gordon G. Wallace 'Determination of Organotins in Fish and Sediments by Gas Chromatography with Flame Photometric Detection' by Isabel Martin-Landa, Fernando de Pablos and lain L. Marr 'Flow Injection Determination of Organosulphur Compounds with Chemiluminescence Detection' by J. Steven Lancaster and Paul J. Worsfold 'Arsenic Speciation by Hydride Generation Atomic Absorption Spectrometry and its Application to the Study of Biological Cycling in the Coastal Environment' by S. D. W. Comber and A. G. Howard 'Selectivity Studies in Supercritical Fluid Chromatography' by M. Martin Sanagi and Roger M. Smith 'Retention Prediction in RP-HPLC Using a Functional Group Database and Expert System (CRIPES)' by Christina M.Burr and Roger M. Smith 'The Determination of Quantum Efficiencies of Laser Dye Using the Thermal Lens Effect' by Jun Shen and Richard D. Snook 'Analysis of Sodium in Blood Plasma Using a New Mini Ion-selective Electrode' by Martin Telting-Diaz, Malcolm R. Smyth, Dermot Diamond, Eileen M. Seward, Gyula Svehla and Anthony M. McKervey 'A Semi-continuous Flow Method for the Trace Analysis of Dissolved Inorganic Antimony' by A. T. Campbell and A. G. Howard Typeset and printed by Black Bear Press Limited, Cambridge, England January 1989 Analytical Proceedings CONTENTS continued inside back cover ... ANALYTICAL PROCEEDINGS, JANUARY 1989, VOL 26 111 34 'The Capillary Gas Chromatography - Atomic Absorption Spectrometry of Organotin and Organolead Compounds' by R.C. Foster and A. G. Howard 37 Equipment News 40 Conferences and Meetings 41 Courses 43 Analytical Division Diary Analytical Applications of Spectroscopy Edited by C.S.Creaser, Uniwrsify of East AngZicZ and A.M.C. Davies, lnsfitufe of Food Research, Nurwich This new book provides a 'State-of-the-Art' review of the applications of the major spectroscopic techniques and will prove invaluable to researchers involved in this form of analysis. The book provides wide-ranging coverage of recent developments in analytical spectroscopy, and in particular the common themes of chromatography - spectroscopy combinations, Fourier transform methods and data handling techniques. Each section includes a review of key areas of current research, written by spectroscopists who have made major contributions in their respective disciplines, as well as short reports of new developments in these fields. These common themes have played an increasingly important part in recent advances in spectroscopic techniques and emphasise the multidisciplinary approach of present research. ROYAL SOCIETYOF 502 pages ISBN 0 85186 383 3 Price S47.50 ($99.00) CHEMISTRY Services hformation To order or for further information, please write to: Royal Society of Chemistry, Distribution Centre, Blackhorse Road, Letchworth, Herts SG6 lHN, UK. or telephone (0462) 672555 quoting your credit card details. We now aFcept Access/Visa/MasterCard/EuroCard. RSC Members are entitled to a discount on most RSC publications and should write to: The Membership Manager, Royal Society of Chemistry, 30 Russell Square, London WClB 5DT, UK.

ISSN:0144-557X    

DOI:10.1039/AP98926BX003

出版商:RSC    

年代:1989

数据来源: RSC

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16 ANALYTICAL PROCEEDINGS. JANUARY 1089. VOL 26 Determination of Organotins in Fish and Sediments by Gas Chromatography with Flame Photometric Detection Isabel Martin-Landa, Fernando de Pablos and lain L. Marr Department of Chemistry, University of Aberdeen, Meston Walk, Old Aberdeen AB9 2UE Organotin compounds, particularly tributyltins (TBT), are used as the active components in antifouling paints for vessels and structures immersed in sea water. Because of their high toxicity they are the focus of increased concern as marine pollutants. The effective concentration of tin in the water on the antifouling paint surface approaches 1 pg ml-1, which is sufficient to prevent fouling organisms (algae or barnacles) from attaching themselves. However, very much lower concen- trations, v i z .. about 1 pg 1-1 in sea water, are lethal to the larvae of many non-target invertebrates. 1 Even lower concen- trations can affect the growth rate and reproduction of commercial shellfish.2 Because of these problems, the retail sale of TBT-containing paints was prohibited by the govern- ment in the Spring of 1987. and similar regulations have been introduced in the United States and France.3 TBT treated netting has been used on salmon farms. As farmed salmon are harvested after about 3 years, there are still fish in the farms that have been exposed to tributyltin. On the other hand, organotin compounds undergo degradation in the environment and in micro-organisms to give, eventually, non-toxic tin(1V). In addition, methylation reactions have also been reported,l.j leading to the possibility of obtaining various organotins.Depending on the pH and salinity, a certain amount of the organotins in water may be adsorbed on to particles and reach soils and sediments. presenting a hazard to marine species which live in, or lay eggs in, those sediments. I n all these types of samples in which organotins may be present. the concentra- tions of organotins are usually lower than 1 pg ml-1 and the matrices are complex. Hence, there is a need for highly sensitive methods for the determination of organotins in order to be able to monitor the levels of toxic organotins or to obtain information on their fate in the environment. Gas chromatography with flame photometric detection6.7 is a very good approach which provides the high sensitivity and good selectivity required for the determination of organotins in complex matrices such as fish tissue and sediments.The method consists of the following steps: ( 1 ) digestion of the sample; (2) extraction of the organotins from the acid digest; (3) chemical derivatisation to obtain derivatives that have higher vapour pressures; (4) separation by gas chromato- graphy; and ( 5 ) measurement of tin in the emission of the Sn-H species in the flame photometric detector (FPD). Several problems arose when we used this method. Taking into account concentrations of the organotins in the samples, the analyses were run for 5-25 g of sample and the final extract was made up to 1 ml. This means that several coextractives, mainly fats and oils, were present at a high concentration in the aliquots injected into the gas chromatograph, giving problems when their retention times were similar to those of the organotins.After overcoming these problems the method was applied to the determination of tributylin and its degradation products (dibutyltin, monobutyltin and the methyl derivatives) in salmon liver and sediments. Experimental Apparatus A Shimadzu GC8AFP gas chromatograph equipped with a flame photometric detector with an EM1 9601B photomulti- plier (range 300-800 nm. maximum at 380 nm), a 610-nm interference filter (Infrared Engineering) and a glass capillary column (12 m x 0.53 mm i.d. coated with a 3.0-um film of BP-1) was used. The injector and detector were held at 250 "C and the column was temperature programmed from 50 to 250°C at a heating rate of 10°C min-1.Nitrogen was used as the carrier gas at a flow-rate of 8.5 ml min-1 through the column and of 37 ml min-1 through the splitter. The detector was operated with a hydrogen-rich flame, the hydrogen and air flow-rates being 50 and 85 ml min-I. respectively. The detectorANALYTICAL PROCEEDINGS. JANUARY 1989. VOL 26 17 output was collected on a Pye Unicam PU4810 computing integrator. Aliquots of 5 yl were injected and peak heights were recorded. The amount of each organotin present was determined from suitable caiibration graphs using Me2PezSn as the internal standard. Reagents and Standards All reagents were of analytical-reagent grade or better. The purity and stability of the standards were checked by GC - FID and GC - FPD under the same operating conditions as those described above.All glassware was washed with aqua regia, doubly distilled water, ethanol and diethyl ether in that order. Standard stock solutions of the internal standard, Me2SnC12 (about 279 (1-g ml-1). were prepared in absolute ethanol. Procedure Weigh accurately between 5 and 25 g of wet salmon liver or sediment into a 250-ml separating funnel fitted with a PTFE tap. Add 40 ml of concentrated hydrochloric acid, shake for 2 h and leave to stand for a further 2 h . Then add 10 ml of hydrobromic acid (48%) and after 15 min extract the mixture with 100 ml of a 0.05% (mlv) solution of tropolone in pentane by shaking vigorously for 2 min. After 1 h separate the organic layer and dry it over anhydrous magnesium sulphate.Place the dried organic layer in a 250-ml round-bottomed flask together with a suitable amount of the internal standard (about 3 pg of Me2SnCI2). Wash the magnesium sulphate with 5 ml of diethyl ether and add this to the organic phase. To the dried organic extract add 20 ml of 1 M pentylmagnesium bromide in diethyl ether and reflux the mixture, with constant stirring. for 1 h . Destroy the excess of Grignard reagent by slowly adding 25 ml of 1 N sulphuric acid. Separate the organic phase and extract the aqueous phase with two 10-ml portions of diethyl ether. At this point add 100 ml of 3% sodium hydroxide solution to the organic phase, shake for 5 min and allow to stand overnight. 7 1 Fig. 1. Micro-evaporator Filter the organic phase into a 250-ml round-bottomed flask and concentrate it on a rotary evaporator under reduced pressure at room temperature to a volume of about 2 ml.Transfer this liquid into a micro-evaporator (Fig. 1). rinsing the walls of the flask with 5 ml of diethyl ether and concentrate to 1 ml under a stream of nitrogen. Use 5-p1 aliquots for the GC analysis. Results and Discussion Digestion and Extraction The use of concentrated hydrochloric acid for the digestion of samples containing organotin compounds has been reported already.8 Previous studies carried out in our laboratory have shown that no loss of the organotin compounds occurs during the treatment with concentrated hydrochloric acid; hence this acid was chosen for the digestion of the samples. The organotins were extracted from the acid digest into a tropolone solution in pentane.Tropolone was used to prevent the loss of highly polar organotins, i . 4 . . BuSn3+. Hydrobromic acid enhances the recovery of the butyltin species," probably because it aids the desorption of these species from the glass wall of the vessel. Derivatisation Procedure The n-pentyl derivatives were prepared, by means of a Grignard reaction, because some of the ethyl and propyl derivatives are sufficiently volatile to be lost during the routine concentration procedures. Derivatisation was carried out under reflux (about 40°C) to ensure quantitative reaction of the di- and monoalkyltins. If the magnesium used to prepare the Grignard reagent is contaminated with metallic tin, then tetraphenyltin will also be obtained after the derivatisation step.Clean-up The injection of an extract containing large amounts of fats and oils. 4.g.. from fish tissue or some types of sediments, into the gas chromatograph could lead to several problems such as background interference and serious damage to the column and detector. Despite the high selectivity of the flame photometric detector (FPD) towards tin-containing com- pounds, it was found that direct injection of an extract from fish tissue into the column gave chromatograms which contained a very large background interference in the range of retention times where the organotin compounds appeared [Fig. 2(ci)]. Ib) 0 5 10 15 20 0 5 10 15 20 Time min Fig. 2. ( a ) Chromatogram of a fith digest not treated with 3% NaOH solution ( h ) Chromatogram of a fish digest alter treatment w i t h 3% NaOH solution Also, the behaviour of the detector changed notably after the injection of such a contaminated sample, resulting in base-line drift.For these reasons, a clean-up procedure was necessary prior to injection of the samples. As the main components of the fish extract will be natural oils and fatty acids. their18 conversion into water-soluble substances by hydrolysis with sodium hydroxide was envisaged as being suitable. Treatment of the fish extract with a 3% (rnlv) solution of sodium hydroxide was found to be very effective in eliminating all potential interferences [Fig. 2(6)]. Concentration After the extraction and derivatisation steps the organotins were contained in a very large volume (-120 ml) of solution and at a low concentration and so a concentration step was necessary.Concentration of the samples by rotary evaporation in a Wheaton flask was attempted first in order to try and avoid the use of a number of different flasks with consequent losses of organotins. However, this technique was very difficult to perform because of continuous bumping of the solution through the system. A Kuderna - Danish concentrator was also tried but the process was very time consuming and was also rejected. Concentration to a volume of 1 ml was carried out, first in a rotary evaporator and then in a cylindrical flask which ended in a narrow calibrated tube (Fig. 1). Determination of Organotins in Salmon Liver To test the utility of the proposed method several salmon liver samples, obtained from a salmon farm and from experiments on the accumulation effects of tributyltin (carried out in the Marine Laboratory at Aberdeen), were analysed.The results are presented in Table 1, while Fig. 3 shows the chromatogram of one of the samples. 1 I JJ - I 5 k 1 1 0 5 10 15 20 Tirnelrnin Fig. 3. Chromatogram of a salmon liver sample. 1, MezSnPez (internal standard); 2. Bu,SnPe; 3, Bu,SnPe,; 4, BuSnPe,; and 5 , Pe,Sn Determination of Organotins in Sediment The same procedure was applied to the determination of organotins in a sediment. The results obtained were: Bus++, 2.17; Bu2SnZ+, 3.72; BujSn+, 0.64; Me2BuSn+, 12.92; and MeBu2Sn+, 11.06 p.p.m. The corresponding chromatogram is shown in Fig. 4. Conclusions The proposed method is suitable for either environmental analysis or laboratory studies on the degradation effects of small amounts of organotin compounds.From the analysis of salmon liver samples it is obvious that degradation of tributyl- tin by debutylation to give di- and monobutyltin occurs. However, it is difficult to conclude whether this degradation ANALYTICAL PROCEEDINGS, JANUARY 1989, VOL 26 actually takes place in the liver or in the water in which the salmon are living. Similar conclusions can be drawn from the results of the organotin analysis in sediments, the most notable feature of the analysis being the high concentration of methyl derivatives found in the sediment sample. The method used Table 1. Concentration of organotin species in salmon liver Organotin/pg g- 1 Sample BuSn3+ BuzSn'+ BuzSn + 1 0.54 2.01 0.38 2 0.24 1 .oo 0.28 3* 0.22 0.59 4.01 4* 0.04 0.05 0.13 5* 0.21 0.33 0.21 6 0.56 0.27 0.85 7 0.64 0.42 1.39 * Concentration experiments in tanks with: 1.0 (3); 0.1 (4); and 1.0 ( 5 ) pg g-1 of TBT in the water.~ here (GC - FPD) is more time consuming than other methods available for TBT ( e . g . , GF-AASX), but it provides consider- ably more information on the degradation and behaviour of these compounds in the environment. Lower values for the concentration of TBT in samples are usually obtained with GC - FPD than with GF - AAS as the latter is based on a final 0 4 8 12 16 20 24 Ti rne/rn i n Fig. 4. Chromatogram of sediment sample. 1. Me2BuSnPe; Me2SnPez (internal standard); 3, MeBu?SnPe; 4. Bu,SnPe; Bu,SnPe,; 6, BuSnPe,; and 7, Pe$n 2, 5 , measurement of the inorganic tin content.A similar result has been found by Short.3 In our view, contamination or poor selectivity during the extraction procedure can cause more serious errors in the GF - AAS method. 1. 2. 3. 4. 5. 6. 7. 8. 9. References Hall, L. W., and Pinkney. A . E., Crit. Rev. Toxicol., 1985, 14. 159. Alzieu, C.. Heral, M., Thiband, Y., Dardignac. M. J . , and Feuillet, M., Red. Trav. Inst. Pech. Marit., 1982. 45, 101. Short, J . W . , Bull. Environ. Contam. Toxicol., 1987, 39, 417. Fanchiang, Y. T., and Wood, J . M.. J . Am. Chem. SOC., 1981. 103, 5100. Hallas, L. E., Means, J . C., and Cooney, J . J . , Science, 1982, 215, 1505. Braman, R. S . , and Tompkins. M. A . , Anal. Chem., 1979, 51, 12. Maguire, R.J . , and Huneault, H . , J . Chromatogr., 1981, 209, 458. Mackie, J . C., Anal. Chim. Acta, 1987, 197, 303. Meinema, H. A . , Burger-Wiersma, T . , Verluis-de Haan, G., and Gevers, E. Ch., Environ. Sci. Technol.. 1978. 12, 288.ANALYTICAL PROCEEDINGS, JANUARY 1989, VOL 26 - Carrier stream Flow Injection Determination of Organosulphur Compounds with Chem ilum inescence Detection hotomultiplier - Chart tube recorder J. Steven Lancaster and Paul J. Worsfold School of Chemistry, University of Hull, Hull HU6 7RX Certain chemical reactions (usually oxidation reactions) yield products in an electronically excited state. which can return to the ground state by emitting a photon, as shown below: A + B + P* + P + light This process is known as chemiluminescence and its efficiency can often be increased by using a suitably fluorescent molecule.which has an excitation spectrum overlapping the emission spectrum of the donor molecule. This is shown below: A + B + S + P * + S - - + P + S " - S + l i g h t The intensity of the emission is proportional to the rate of the reaction; therefore. chemiluminescence can be used for quantitative analysis. Examples of chemiluminescence analysis include the cobalt catalysed oxidation of luminol the determination of mor- phine by its oxidation with permanganate3.' and the determina- tion of fluorescent molecules by the peroxyoxalate reacti0n.i Flow injection analysis (FIA) provides a useful experimental system for the study of chemiluminescence reactions because it permits rapid and reproducible mixing of the sample and reagents.The transient chemiluminescence emission can be detected by suitable control of the flow-rate and flow-cell volumeh and a sample throughput of >120 h-1 is typical. 1. Sensitivity. Extremely sensitive analyses are often possible because the absence of a source eliminates scattering and noise associated with the lamp. Also, there is little or no background emission. 2 . Wide dynamic range. I n chemiluminescence analysis, calib- ration data are often linear over several orders of magnitude, e . g . . the calibration data for morphine are linear from 10-4 to Preliminary work showed that certain organosulphur com- pounds exhibited chemiluminescent emission when mixed with sodium hypochlorite. This paper describes the optimisation of a flow injection procedure for the liquid phase chemilumines- cence determination of 2-(ethy1thio)phenol and structurally related molecules.The advantages of chemiluminescence include: 10-10 M . 3 Experimental Fig. 1. shows the flow injection system used for the determina- tion of 2-(ethy1thio)phenol. The carrier stream was acetone and the oxidant stream was 1 . O M sodium hypochlorite in 0.1 M hydrogen carbonate buffer at pH 11.0. Each stream was pumped at 1.0 ml min-1 by a peristaltic pump (Gilson Minipuls 2: Pl), interfaced to a microcomputer (BBC). Teflon tubing (0.8 mm i.d.) was used throughout the remainder of the manifold. Standards were injected into the acetone carrier stream using a rotary valve (Rheodyne 5020) with a 50-ul sample loop. The valve was operated by an electrically activated switching device (Anachem) interfaced to the micro- computer.2-(Ethy1thio)phenol standards in acetone covering the range 1 x 10-3-1 x 10-1 M were prepared. Standards were drawn into the sample loop by means of a second peristaltic pump (Ismatec Mini S840; P2) which was also interfaced to the microcomputer. The standard and oxidant were mixed at a PTFE T-piece and the chemiluminescence emission occurred in a 177-pI glass coil (1.5 mm i.d.). The distance between the injection valve and the T-piece was 25 cm and between the T-piece and the glass coil 2.5 cm. The light was detected by a photomultiplier (Thorn EM1 Type 9789 QB) and the output recorded on a chart recorder (Chessell BD 4040). The reaction conditions stated above were used for all experiments and all results are the means of five injections unless stated otherwise.Autosampler Injection , 0 uooo valve \ Reagent % 4 i ~ l o w cell stream Waste Peristaltic Pumps Fig. 1. Flow injection manifold Results and Discussion A series of experiments were carried out to establish the optimum conditions for the flow injection procedure. The effect of the oxidant concentration at pH 11.0 was investigated using a 5 x 10-2 M 2-(ethy1thio)phenol standard. Hydrogen peroxide and sodium hypochlorite were used as the oxidants and the results are shown in Table 1. The most intense emission occurred with 2 M sodium hypochlorite. although in subsequent experiments a concentration of 1 M was used to conserve the reagent. Table 1. Effect of oxidant concentration E rn i ss i o n i n t e nsi t y /m V Oxidant conce n t r a t i o ni hi 0.001 0.01 0 .1 0.2 0.5 1 .o 2.0 3 . 0 4.0 With hydrogen peroxide 0 0 1 . 1 2.0 3.0 9.5 2.3 2.2 - With h y poc h I o r i t e 2.0 2.6 18.9 29.5 31.5 37.2 28.4 - - The effect of pH was investigated using 1 M sodium hypochlorite and a 5 x 10-2 M 2-(ethy1thio)phenol standard. The pH was varied from 8.0 to 13.0 and the results obtained are shown in Table 2. The maximum intensity occurred at pH 1 1 .(I. The effect of using different solvents for the standard solutions was also investigated. Acetone was found to be the best solvent of those investigated and gave an emission intensity of 103.5 mV for a 5 x ~ O - ' M 2-(ethylthio)phenol standard; methanol. propan-2-01. ethanol and propan-1 -01 gave signals of 68.1, 38.8.38.6 and 19.4 mV.respectively. The20 Table 2. Effect of pH PH Emission intensitylmv 8.0 9.0 9.0 9.2 10.0 12.2 10.5 18.5 11 .o 23.9 11.5 19.8 12.0 14.8 12.5 13.9 13.0 13.6 reduction in intensity observed on going from acetone to propan-1-01 may be due to an increase in the degree of hydrogen bonding of the solvent which restricts the access of the oxidant. Several other compounds were investigated in an attempt to elucidate the structural features necessary for chemilumines- cence to occur. 2-(Ethy1thio)phenol gave the most intense emission with a relative intensity of 100. p-(Ethy1thio)benzoic acid and p-ethylphenol gave relative emission intensities of 3.8 and 0.6, respectively. 0- and m-Ethylphenol, ethylbenzene and phenol gave negligible emissions, indicating that chemilu- minescence is due to the oxidation of divalent sulphur.The emission intensity of 2-(ethy1thio)phenol is much greater than that of p-(ethy1thio)benzoic acid. This may be caused by intramolecular hydrogen bonding in 2-(ethylthio)phenol, which makes radiationless deactivation less probable. The calibration data for 2-(ethy1thio)phenol are given in Table 3. Using a log - log plot of concentration I-rersiis emission intensity the response is linear over the range 1 x 10-3-5 x 10-2 M ( r = 0.997). The theoretical detection limit is4 x 10-4 M (20 above the background signal). Future work will include the development of totally non- aqueous systems using oxidants that are effective in organic media. This should improve the precision and reduce the problems associated with reproducible mixing and precipita- tion of the analyte when an aqueous stream is mixed with an organic stream. ANALYTICAL PROCEEDINGS.JANUARY 1989. VOL 36 Conclusions Flow injection analysis is an ideal technique for monitoring chemiluminescence reactions. Certain organosulphur compounds exhibit solution phase chemiluminescence and their emission intensities are dependent on their structure. The chemiluminescence emission intensity is influenced by the nature of the solvent. The limit of detection for 2-(ethy1thio)phenol is 0.3 mM (20 nmol). Table 3. Calibration data for 2-(ethylthio)phenol Concentration/ Emission RSD. "!o M in tensi t y/mV ( n = 10) 0 0 0 1 x 10-3 0.2 22.8 5 x 10-3 2.3 2.9 1 x 1 0 2 7.6 6.2 2 x 10-2 22.1 2.6 5 x 10-2 150.5 1.6 1 x 10-1 144.3 3.4 The authors thank Thornton Research Centre, Shell Research Limited, for supporting this work.References 1. 2. 3. 4. 5. 6. Boyle, E. A., Handy. B . . and Vangeen. A.. And. Chetn., 1987. 59. 1499. Burguera. J . L.. Townshend. A . , and Greenfield. S.. A n d . Chim. A m . 1980, 114, 209. Abbott. R. W.. Townshend, A . . and Gill. R.. A t z d y r . 1986. 111,635. Abbott, R. W.. Townshend. A.. and Gill. R.. Atui!\.sr. 1987. 112. 397. Sigvardson. K . W.. and Birks. J . W.. And. Chem.. 1983. 55. 432. Rule, G.. and Seitz. W. R.. Clin. Chem.. 1979. 25. 1635. Arsenic Speciation by Hydride Generation Atomic Absorption Spectrometry and its Application to the Study of Biological Cycling in the Coastal Environment S.D. W. Comber and A. G. Howard Department of Chemistry, The University, Southampton, Hampshire The speciation of arsenic in natural waters is indicative of its diverse reaction chemistry and can be used to investigate a number of geochemical and biological processes. There are four commonly reported forms of arsenic in natural waters: ( i ) oxidised inorganic arsenic [ arsenic(V)], believed to be arsen- ate; (ii) reduced arsenic. probably arsenite [arsenic(III)]; (iii) monomethylated arsenic; and (iv) dimethylated arsenic. 1-4 The study of the behaviour of arsenic in the aquatic environment requires the development of methods that can be used to measure routinely arsenic speciation. Such a system must have sufficient sensitivity to permit measurements to be made of species that are present at concentrations below 100 ng I-' while maintaining relatively high precision.As this system is to be used as a survey technique, it must also be rapid and robust. These criteria are largely met by methods that are based on the trapping of arsenic hyrides prior to sequential release into an atomic absorption spectrometer. Such methods are based on the procedures first used by Braman er u1.5 and Andreae.h This paper describes a rapid hydride generation system which has been developed for the speciation of dissolved arsenic by atomic absorption spectrometry. The system is simple to operate, highly reliable in routine use and has been extensively employed in the study of biogeochemical processes governing the speciation of arsenic in estuarine and coastal environments.Experimental Reagents Standard solutions were prepared from arsenic(II1) oxide. the disodium salt of monomethylarsonic acid and the sodium salt of dimethylarsinic acid. A stock mixed standard solution contain- ing 100 mg 1-1 of arsenic as each individual species was prepared using doubly distilled water and this was diluted further to give a daily working standard of 10 pg 1 - 1 . Method The semi-continuous method used here is similar to that described by Howard and Arbab-Zavar7 but with refinementsANALYTICAL PROCEEDINGS. JANUARY 1989. VOL 26 21 that have led to significant improvements in resolution. reproducibility and sample turnover since the original publica- tion (Fig. 1). A peristaltic pump is used to mix the sample with equal volumes of hydrochloric acid ( 1 + 9) and then sodium tetrahydroborate(II1) (2% rnlV).The resulting arsine. monomethylarsine and dimethylarsine then pass into a custom- built gas - liquid separator. The gas stream is dried with sodium hydroxide pellets and trapped on hydrofluoric acid etched glass beads (about 40 mesh) in a U-tube immersed in liquid nitrogen (-196°C). Once all the sample has been taken up, time is allowed for the arsines to be generated and trapped, after which the liquid nitrogen is removed and the trap allowed to warm to room temperature. The arsines are eluted by the nitrogen carrier gas according to their volatility (arsine Peristaltic pump (2.5 rnl rnin-l, all channels) Electrically heated quartz NaOH pellets atorniser tube in path of AAS Nitrogen Sample rl I- 7 HF-ett!hed beads t Waste Fig.1. Semi-continuous hydride generation system for arsenic speciation (not to scale) followed by monomethyl- and then dimethylarsine) into an electrically-heated quartz T-tube placed in the light path of a Baird A5100 atomic absorption spectrometer. The output is recorded on a Tekman TE200 chart recorder (Fig. 2). 1 2 10 cm I 30s Time - Fig. 2. Typical output from hydride generation AAS for a 1-ml sample containing 1 ng of inorganic arsenic. ( 1 ) Inorganic arsenic: (2) monomethylarsenic (MMAS): and (3) dimethylarsenic (DMAS) Arsenite is measured by controlling the pH of the reaction, the hydrochloric acid being replaced by a sodium acetate - acetic acid buffer (0.1 M ) (pH 5.0). Under these conditions.arsenic(II1) forms arsine but not arsenate. I n a previous paper7 the effect of high concentrations of interferents on this method were discussed. In the analysis of estuarine waters. interferences are not generally significant as potentially troublesome dissolved trace elements are normally present at relatively low concentrations. As a precaution. however, standard additions analyses were run occasionally to confirm the absence of interferents. A summary of the system parameters is given in Table 1. Table 1. System parameters Flow-rates and settings Nitrogen carrier gas . . . . . . . . Hydrochloric acid ( 10o/o) . . . . . . Sodium tetrahydroborate( 111) (2% miV) Air . . . . . . . . . . . . . . Sample . . . . . . . . . . . . Sodiumacetate buffer(O.1 M) . .. . Sampling rate . . . . . . . . . . Trapping time . . . . . . . . . . Source . . . . . . . . . . . . Lamp current . . . . . . . . . . Linear range . . . . . . . . . . Sample size . . . . . . . . . . . . Wavelength . . . . . . . . . . . . Furnace temperature . . . . . . . . 160 ml min 1 2.5 ml min I 2.5 ml min- I 2.5 ml min - I 2.5 ml min ~ I 2.5 ml rnin I 2 0 h I 90 s Arsenic hollow-cat hode lamp 8mA 197.3 nm ca. 900 "C (k3 ng 0.25-2.0 ml Procedure The trap is frozen and the clock started: the probe is placed in the sample cup and allowed to take up all of the sample (typically between 250 ul and 2 ml). It is then transferred into a wash solution of distilled water. After 90 s the liquid nitrogen is removed from the trap and the arsines are allowed to vaporise into the atomiser, where they are monitored by the atomic absorption spectrometer. Intermittently the trap is dried with a heat gun to remove the condensed water that builds up after a period of time and which would otherwise cause excessive back-pressure.At the beginning and end of the analysis a calibration of between 0.25 and 1 ng is run with quality control standards being analysed every 4 or 5 samples to ensure accuracy. The over-all performance of the system is presented in Table 2. Table 2. Performance data Average peak height/ Detection limiti Sample* cm RSD. '"0 ng: Arsine . . . . . . 14.22 k 0.65 4.6 0.0 19 Monomethylarsenic . . 9.88 k 0.76 6.1 (1. (J4S Dimethylarsenic . . 6.3 -t 0.32 5.1 0.061 Blank(AsH3) . . . . 1.3 f 0.05 3.8 * Ten replicates. + Detection limit defined as three times the standard deviation otthe blank.Typical Application The technique was used in a number of studies of arsenic in estuarine. coastal and oceanic environments. In the example described here, the method has been used to investigate factors that influenced the speciation of arsenic in Southampton Water during 1987. Samples were collected regularly throughout the year. with particular attention being paid to the warmer months when biological activity was high. At the same time, bacteria and phytoplankton populations were monitored by members of the Oceanography Department. Only arsenic(V) was present in the water all year round. Arsenite, monomethyl- and dimethylarsenic were only present in significant amounts from mid-May to the end of October, the period during which biological activity reached its maxi- mum.This confirmed our previous observations regarding speciation seasonality.x-10 Dissolved monomethylarsenic and dimethylarsenic levels reached a broad maximum in July and August. The thermodynamically unstable arsenite peaked early in the summer (18th May). when it accounted for over22 ANALYTICAL PROCEEDINGS. JANUARY 1980, VOL 26 50% of the total inorganic arsenic present. This coincided with a bloom of filamentous algae. The results are illustrated in Fig. 3. 1.2 1 .o 0.8 c - 0.6 I I 2 0.4 0.2 0 R I \ " I m Y- Y u - E 3 7 87 26,8,87 19 10 87 Date Fig. 3. Arsenic speciation during the 1987 temporal survey at Calshot Buoy. Southampton Water. UK. (A) AsV; (B) As"'; (C) MMAS; and (D) DMAS This work is only a small part of an ongoing project designed to study the behaviour of arsenic in a number of estuarine and coastal systems in order to clarify the relationship between the speciation of dissolved arsenic and biological activity in the water column.The authors thank the National Environment Research Coun- cil and Dr. A. Morris of the Plymouth Marine Laboratory for their support of this work. 1 . 2. 3 . 4. 5 . 6. 7. 8. 9. 10. References Sanders. J . G., and Rapp. P.-V., Reun. Cons. In!. Esplor. Mer.. 1986. 186, 185. Sanders. J. G.. Mar. Chem., 1985, 17, 329. Andreae. M. O., and Froelich, P. N.. TellirJ, 1984, 36B. 101. Andreae. M. O., Limnol. Oceunogr., 1970. 24. 440. Braman, R. S., Johnson. D . L., Foreback, C. C.. Arnrnons, J . M., and Bricker.J . L.. And. Chem.. 1977, 49, 621. Andreae, M. 0.. Anul. Chem., 1977, 49. 820. Howard, A. G., and Arbab-Zavar. M. H . , Anulw. 1981. 106, 213. Howard, A. G.. Arbab-Zavar, M. H.. and Apte. S. C.. Mar. Chem., 1982. 1 1 . 393. Howard. A. G., Arbab-Zavar. M. H.. and Apte. S. C.. Estuarine Coustal Shelf Sci., 1984. 19. 493. Apte, S. C.. Howard, A. G., Morris. R. J . . and McCartney. M. J . , Mar. Cheni., 1986, 20. 119. Selectivity Studies in Supercritical Fluid Chromatography M. Marsin Sanagi and Roger M. Smith Department of Chemistry, Lough boroug h University of Tech no logy, Loug h boroug h, Leicestershire L E I ? 3TU There has been a considerable interest in supercritical fluid chromatography (SFC) in the last few years as an alternative instrumental analytical technique complementary to high-per- formance liquid chromatography (HPLC) and gas - liquid chromatography (GLC).' SFC has been gaining acceptance in a wide range of areas in both analytical and industrial chemistry, particular for petrochemicals and pharmaceuticals. 1 As with HPLC and GLC, the retention and selectivity of the solute in SFC depend on the conditions used for the separation, including the pressure. temperature and stationary phase composition of the mobile phase.However, in contrast to HPLC, the density of the mobile phase, which is determined by pressure and temperature, also plays an important role in dictating retention. This gives additional flexibility when optimising separations in SFC and offers an alternative selectivity to other techniques.Good instrumentation is a prerequisite for performing sound chromatographic separations. However, good instrumentation alone will not provide the required separation without a sensible choice of the operating conditions and, in this respect, some knowledge of the retention behaviour of the solute will provide a valuable guide to achieving such separations. I n both GLC and HPLC the use of relative measurements is well established as a method of reducing the effect of small changes in the operating conditions. These measurements can either be relative to a single standard or to a retention index scale obtained using a series of homologous standard com- pounds. In GLC an excellent retention index system for n-alkanes has been proposed by Kovats,2 based on a constant increment in the logarithm of the capacity factor ( k ' ) with the length of the carbon chain (log k' = aC,, + h).The retention index of the n-alkane standards is defined as the carbon number x 100 and the values for test compounds are calculated by interpolation between standards. A similar concept has also been used in reversed-phase HPLC. but usually alkyl aryl ketones3 or alkan-2-onesj have been used as the standard compounds as the n-alkanes are highly retained compared with most analytes and they are not detectable by the commonly used spectroscopic detectors. In contrast, the alkyl aryl ketones are readily detectable by ultraviolet detectors and cover a wide retention range of most compounds of medium polarity. and consequently they have been used as a means of drug identification.5 This paper describes an investigation into the retention behaviour and selectivities of different groups of compounds with changes in the operating parameters and provides a detailed study of the use of different sets of standards as the basis of retention indices in SFC.Experimental The supercritical fluid chromatograph used in this work has been described elsewhereh; it consists of a modified Jasco BIP-1 HPLC pump and a Pye Unicam 104 gas chromatograph. A 150 X 4.6 mm i.d. column packed with PLRP-S 5 pm polystyrene divinyl benzene (PS-DVB) (Polymer Labora- tories) was used. Acetone was used as the dead-volume marker. Retention indices based on either alkyl aryl ketones or n-alkanes were calculated by fitting the log k' versus carbon number x 100 data for the standard compounds to a regression line and then interpolating the log k' values for the test compounds. Results and Discussion Retention Index Scales The alkyl aryl ketones and n-alkane homologues were eluted in order of increasing relative molecular mass and so theANALYTICAL PROCEEDINGS.JANUARY 1989. VOL 26 separations followed a reversed-phase type of retention mechanism (Fig. 1). Almost linear relationships between log k' and the carbon number was found although there appeared to be some deviation for the first two members of each series. The slopes of the relationship of log k' versus carbon number x 100 for the alkyl aryl ketones and n-alkanes were similar but not identical, suggesting that the addition of a methylene group does not have the same effect on the retentions of the two homologous series.Because a flame ionisation detector cannot be used when a modifier is added to the mobile phase and spectroscopic detectors are needed. the n-alkanes are unsuit- able for general use as SFC retention index standards. The retention index scale based on the alkyl aryl ketone homolo- gous series has therefore been used to compare the selectivities of different column materials with changes in the operating parameters, by measuring the retention of alkylbenzenes and a set of model compounds with different functional groups. 1 1000 1500 2000 Carbon number x 100 Fig. 1. Plot of log k ' for n-alkanes and alkyl aryl ketones \'crsiis carbon number x 100. Conditions: column, PLRP-S; temperature, 60°C; and mobile phase.carbon dioxide. (A) Alkyl aryl ketones; and (B) n-alkanes Effect of Pressure In general, the retention of a compound in SFC decreases with an increase in pressure but the relationship is not linear (Fig. 2). This is because the solvating power, which is roughly proportional to the density, increases non-linearly with an increases in pressure.' The relative retention of compounds in the homologous series did not change as shown by the graphs of log k' versus pressure for both the alkyl aryl ketones and alkylbenzenes. J 2000 2200 2400 2600 2800 Mean column pressureAb Fig. 2. Variation of log k' for alkyl aryl ketones and alkylbenzenes as a function of pressure. Conditions: column, PLRP-S; temperature, 60°C; and mobile phase, carbon dioxide.(A) Propylbenzene; (B) butylbenzene; (C) acetophenone; (D) propiophenone; (E) butyrophe- none; (F) valerophenone; (G) hexanophenone; and (H) heptanophe- none The retention indices, based on alkyl aryl ketones, of the model compounds were determined and plotted as a function 23 of the pressure (Fig. 3). A range of different behaviours was observed. The retention indices for benzaldehyde and methyl benzoate remained almost constant as the pressure was increased which suggests that these compounds have a similar retention behaviour to alkyl aryl ketones. On the other hand, as the pressure was increased the more polar compounds such as benzoic acid, benzamide and p-cresol were retained to a greater extent relative to the alkyl aryl ketones. This effect can be attributed to the decreasing solubility of these polar compounds in the mobile phase. / 2000 r .- : I 500 2000 2200 2400 2600 2800 Mean column pressureilb i n - 2 Fig.3. Variation of retention indices. based on alkyl aryl ketones, ot model compounds with increasing pressure. Conditions: column, PLRP-S; temperature, 60 "C; and mobile phase, carbon dioxide. (A) Benzaldehyde; (B) methyl benzoate; (C) benzyl alcohol; (D) p-cresol; (E) N-propylaniline; (F) benzoic acid; (G) benzamide; and (H) benzylamine Effect of Tern pera tu re The retention behaviour of different groups of compounds with changes in the operating temperature was studied. At a constant pressure above the critical point, increasing the temperature effectively decreases the density of the mobile phase and hence the over-all elution strength and, as expected, the retention increased for all compounds (Table 1).It was also found that changes in temperature could bring about relative selectivity changes between compounds with different func- tionalities and that at some points the elution order of the compounds could be reversed, e . g . , for p-cresol and N-propyl- aniline. Table 1. Capacity factors of model compounds at different tempera- tures. Conditions: column, PLRP-S, 5 pm; mean column pressure, 2515 Ib in-?; flame ionisation detection; mobile phase, carbon dioxide Capacity factor Tempera t u re/"C (Eluent densitylg cm- 3 ) 40 Compound (0.81 1) Benzaldehyde . . . . 1.27 Methyl benzoate . . . . 1.45 Benzylalcohol . . . . 1.87 Nitrobenzene . . . . 1.95 p-Cresol .. . . . . 3.19 N-Propylaniline . . . . 3.02 Benzoic acid . . . . . . 5.54 Benzamide . . . . . . 7.78 Benzylamine . . . . . . 12.50 60 (0.673) 1.51 1.70 2.13 2.31 3.25 3.31 5.61 8.70 14.26 80 (0.5 1 9) 2.04 2.34 2.77 3.19 3.96 4.26 6.96 11.14 20.70 100 (0.406) 2.72 3.32 3.65 4.42 4.86 5.81 7.99 14.12 32.2324 c1 d 0 H u ANALYTICAL PROCEEDINGS. JANUARY 1989, VOL 26 Effect of Modifier One of the drawbacks of using carbon dioxide as the mobile phase is that because of its low polarity, it is difficult to elute polar compounds. The separations of these compounds are typically characterised by very broad, tailing peaks, which lead to poor reproducibility of the retention time and peak area and poor sensitivity.' The use of organic modifiers in the carbon dioxide mobile phase was therefore investigated.A series of separations was carried out on the PLRP-S column with different percentages of methanol over the range 0-14.6%. The addition of a low percentage of methanol was found to reduce drastically some of the retentions. The modified eluent generally gave better separations and peak shapes for the polar compounds, particularly for the more polar compounds, benzoic acid, benzamide, benzylamine, and the alcohols. These results confirm previous reports detailing the drastic effects on packed column SFC of the addition of small amounts of a modifier to the carbon dioxide mobile phase. 8." The retention indices of the model compounds were determined and the values plotted as a function of the methanol concentration in the mobile phase (Fig.4). Marked selectivity changes were observed when the amount of modifier in the mobile phase was varied. The retention indices of the 1500 tv X -0 .- : 1000 .- c C al c. a 500 0 4 a 1 2 16 Methanol, '10 VN Fig. 4. Variation of retention indices, based on alkyl aryl ketones. of selected compounds with methanol concentration. Conditions: col- umn. PLRP-S; mean column pressure, 2515 Ib in-'. (A) Toluene; ( B ) methyl benzoate; (C) benzyl alcohol; (D) p-cresol; (E) N-propylani- line; (F) benzoic acid; ( G ) benzamide; and (H) benzylamine more polar compounds, benzoic acid, benzamide and the aromatic alcohols and phenols. decreased with an increase in the modifier concentration. In contrast, those of the non-polar compounds, toluene and methyl benzoate, were virtually unchanged or increased only slightly.Surprisingly, the rela- tively polar amines, benzylamine and N-propylamine. showed little change on this polymer column. Effect of Stationary Phase Similar experiments were also carried out using ODs- and cyano-bonded silica columns. The most marked difference was in the behaviour of amines such as benzylamine, which was highly retained on ODs-silica. This was presumably due to silanol interactions as the retention of these compounds decreased markedly with the addition of small amounts of modifier to the mobile phase. The cyano-silica columns showed greater retention of the more polar compounds and less retention of the non-polar compounds compared with the corresponding separations performed on ODs-silica or poly- mer columns.Conclusions The retention and selectivity in SFC varies with the operating pressure, temperature, density and composition of the mobile phase and stationary phase. Any one or a combination of these factors can be used to vary the selectivity of the system in order to optimise the separation. Retention indices were used as a convenient means of recording the variation in the selectivity with changes in the operating parameters. We thank Polymer Laboratories Ltd. (UK) for the generous gift of the PLRP-S column and the Public Services Department and the University of Technology, Malaysia. for a studentship to M.M.S. 1. 2. 3 . 4. 5 . 6. 7. 8. 9. References Smith, R. M.. Editor. "Supercritical Fluid Chromatography." RSC Chromatography Monographs, Volume 1.Royal Society of Chemistry, London, 1988. Kovats, E . . Helv. Chim. Acta, 1958. 41. 1915. Smith. R. M.. J. Chromutogr.. 1982. 236. 313. Baker, J . K.. and Ma. C. Y . . J . Chromatogr.. 1979. 169. 107. Smith, R. M.. Ad\!. Chromatogr.. 1987. 26. 277. Sanagi. M. M.. and Smith. R. M.. Anal. Proc.. 1987. 24. 304. Schoenmakers. P. J., Rothfusz. P. E.. and Verhoeven. F. C. C . J . G.. J . Chromarogr.. 1987. 395. 91. Blilie. A. L.. and Greibrokk. T.. And. C'hem.. 1985. 57. 2239. Levy, J . M.. and Ritchey. W. M.. J. Chromatogr. Sci.. 1986.23. 242. Retention Prediction in RP-HPLC Using a Functional Group Database and Expert System (CRIPES) Christina M. Burr and Roger M. Smith Department of Chemistry, Loughborough University of Technology, Loughborough, Leicestershire LE 1 1 3TU The possibilities of using expert systems in analytical chemistry applications have recently been the subject of a number of publications.'-" It has generally been agreed that expert systems can provide a convenient and user-friendly interface for different situations. Although many methods of prediction have been proposed for reversed-phase high-performance liquid chromatography very few are based on the molecular structure of the analyte.The aim of this work has been to develop a method of calculating the retention time of a compound from its structure. This is expressed as its retention index based on the alkyl aryl ketone scale. 1 ° . l l The calculation uses the equation RI = PI + ZSIR + ZSIAr-X + ZS1R-X + E I I y z where PI = retention index of parent: SIR = substituent index due to saturated alkyl chain; SI,,-X = substituent index of aromatic substituents; SIR_?( = substituent index of aliphatic substituents; and I f y z = interaction indices due to interactions between substituents.Each term in the above equation is related to the eluent composition. in either methanol - bufferANALYTICAL PROCEEDINGS. JANUARY 1089. VOL 26 800 750 X U .E 700 or acetonitrile - buffer, by a quadratic equation: I = ax2 + hx + c (s = '/o organic modifier) The values of the coefficients for a wide range of substituents and interactions have been determined experimentally from the retention indicesl2.13 of a range of model mono- and di-substituted aromatic compounds, over the eluent ranges 4&8O0/o methanol and 30--80°/~ acetonitrile.These include 11 aromatic substituents on benzene and 10 aliphatic substituents on a1 kylbenzenes. including alcohols, halides. cyano groups and acid derivatives, but under the experimental conditions employed free carboxylic acids could not be examined. The data has been used to form a database which is interrogated using an expert system program. The program (CRIPES, Chromatographic Retention Index Prediction Expert System) was written as the knowledge base of a commercial expert system shell (VP-Expert. Paperback Soft- ware). This particular shell can do mathematical calculations and is also capable of communicating with compatible external spreadsheets. The regression equations can therefore be held in the external spreadsheet, enabling them to be updated without extensive modification of the knowledge base.CRIPES has been used to provide a "user-friendly" interface to the database and for the calculation of retention indices. The program will also calculate the resolution between pairs of compounds and can suggest optimum separation conditions for mixtures. The Database The basis of the prediction system is the database collection of the a , b and c coefficients of the quadratic equations for the retention of the parent compound benzene, the substituents and the interaction terms. The individual substituent indices have been calculated from the retention index increments calculated as the difference, at the same eluent composition. between the retention index of a mono-substituted compound and the parent compound benzene (Fig.1). Quadratic regres- sion lines were fitted to the change in experimental retention index increments, with each eluent composition, to obtain the coefficients of the substituent index equations. For all the substituents the quadratic curves were a very close fit to the experimental retention index increments. The coefficients were transferred in each instance to a spreadsheet (VP- Planner, Paperback Software). Interactions which occur between substituents, such as hydrogen bonding. steric interactions and electronic interac- - - - 11501 1 .- 5 900 .- c C 850 1100 c 700 1000 I I I - t - I 750 t I 25 tions, are accounted for by using interaction indices. These are derived from the difference between the measured retention index of a di-substituted compound and the calculated sum of the parent retention index and the substituent indices: For example, the hydrogen bonding in 2-hydroxyacetophe- none considerably reduces the polarity and increases the retention (Fig. 2) so the interaction index can be expressed as A large number of interaction indices have been determined for aromatic substituents in the ortho, meta and para positions to either hydroxyl or methyl groups.These represent com- pounds in which strong electronic interactions would be expected and those in which only weak electronic interactions would be expected, respectively. The interactions vary with eluent composition and the values can also be fitted to quadratic expressions whose coefficients have been entered into a spreadsheet.IZ = RI,,, - ( P I + Z S I ) IIOH+COCHJ = RIcxp - + SIAr-OH -t slAr-COC'ti,) 900 1 .- LT 550 ( g C 0 C " 500 1 I 1 I I 1 ivieLiv concenrrariori, -10 Fig. 2. Determination of interaction indices for H-bonding in 2-hydroxyacetophenone as the difference between the retention index calculated as Rl = PI + ZS/ and the experimental retention index. I, Experimental retention index; 0. calculated retention index from individual i ncrem e n t s . I l O i 1 <.( )c I ~. interact ion index User input name I and substituents present I I 1 Sum PI, SI and II coefficients 1 I 1 Calculate retention indices at 40-80% MeOH and 30-80% MeCN I I DisDlav RI and a m r o x k' 1 Fig. 3. database and calculation of predicted retention indices CRIPES-path of the program steps for interrogation of the Operation of The Expert System (CRIPES) The expert system provides a simple and convenient method for bringing together the coefficients from the spreadsheet and26 ANALYTICAL PROCEEDINGS.JANUARY 1989, VOL 26 Table 1. Example of calculation of retention index Compound name : Thymol Saturated aliphatic carbons : C3H7, CH3 Substituents : Aromatic OH Interaction terms : mOH-R. PhCH-R, secondary CH3 (Coefficients of equations I = ax? + bx + c (x = '/" modifier) Eluent modifier Methanol Acetonitrile Index term PI S I R -CH3 -C3H7 SIAr-Oll I I m OH-R IIPhCll-R ( 2, II\CC-CH3 Sum Calculated Retention Indices Methanol, YO 40 50 60 70 80 a -0.0121 -0.0250 0 0 0.0064 0 - 0.0065 - 0.0372 RLlC 1042 1039 1028 1009 984 b 3.879 0 0 - 1.061 0 0.448 -0.270 C 749 -151 100 300 24 - 24 - 16 2.996 982 R L , 1042 1035 1030 1001 965 a - 0.0 140 0.0243 0 0 0 0 0.0051 - 0.0052 b 2.600 -4.840 0 0 0.150 0 0 -2.090 Acetonitrile.o/o RIG,,, 40 1001 50 984 60 969 70 955 80 94 1 C 845 - 89 100 300 - 26 - 24 - 30 1076 R L , 1005 993 953 955 963 calculating the retention index. The program needs to extract the appropriate coefficients for the parent index, substituent indices and interaction indices for the analyte. By summing the coefficients, the retention index can be expressed as quadratic equations for both methanol and acetonitrile. This enables the calculation of the retention index at eluent compositions within the range 30-80% acetonitrile and 40- 80% methanol. CRIPES produces menus enabling the user to select which aromatic and aliphatic substituents are in the compound.The program will then prompt the user to input the number of each substituent and its position. Following this the program extracts the coefficients of the appropriate substituent interaction equations. The information on which substituents are present and their positions is then used to determine the interactions and to extract the appropriate coefficients for the interaction index equations (Fig. 3). The retention indices for a range of eluent compositions are then calculated and dis- played. By using the relationship between the retention index and the capacity factor log k' = a'RI + 6' it is possible to back-calculate to predict capacity factors from the retention indices. It is also possible for CRIPES to compare the equations for two compounds, calculate the maximum separation and hence suggest optimum separation conditions. An example of the calculation is given for thymol in Table 1.For this compound the substituents are an aromatic hydroxyl group (SIAr-OH), a methyl group and a branched alkyl chain (SIR) on an aromatic ring. In addition, interaction terms are required for the interaction between a meta-substituted hydroxyl and alkyl group (IIm0H-R) and for the substitution on the benzylic carbon group (IIPhCH-R). This has been found to have a different increment from subsequent saturated carbon atoms. Finally, a term is required to account for the differences between the retention behaviour of straight and branched chain isomers (llsec-CHj).14 There was good agreement between the calculated and experimental retention index. The calculations could be carried out by using a calculator; however, this would prove time consuming and could become RI = x2Za + xZb + Zc (x = o/o organic modifier) complicated when several interactions were occurring. It would also be necessary to remember continually all the rules for the interactions and isomer effects, whereas these opera- tions are automatically included in CRIPES. CRIPES has been tested by calculating the predicted retention indices of a number of poly-functional model compounds, which have been compared with the retention indices of these compounds determined experimentally at selected eluent compositions. For most compounds there is, however, good agreement between the experimental and calculated retention indices.However, the database so far only contains parameters for a limited number of interactions between groups and cannot therefore compensate for all the interactions that might occur in some complex compounds. We thank the following: The Science and Engineering Research Council for a research grant and for a studentship to C. M. B., and Phase Separations Ltd. for a gift of Spherisorb ODS-2. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. References Pierce, T. H., and Hohne, B. A.. "Artificial Intelligence Applications in Chemistry," American Chemical Society. Washington, DC, USA, 1986. Bridge, T. P.. Williams. M. H.. and Fell, A. F.. Anal. Proc.. 1988, 25. 43. Ayscough. P. B., Chinnick. S . J . , Dybowski, R., and Edwards.P.. Chem. Ind.. 1987. 15. 515. Frazer, J . W., Mikrochim. Acra, 1986. 11, 163. Kleywegt, G . J . , Lab. Microcomprtr.. 1987, 6. 74. Glajch. J . L., LCGC, 1988, 6, 30. Dessy, R . E . , Anal. Chem., 1984. 56, 1201A. Dessy, R . E., Anal. Chem., 1984. 56, 1312A. Bridge, T. P., Williams, M. H., and Fell, A. F . . Chem. Br.. 1987, 23, 1085. Smith, R. M., Adv. Chromarogr.. 1987. 26. 277. Smith, R . M., J . Chromarogr., 1982. 236. 313. Burr, C. M.. and Smith, R. M.. Anal. Proc.. 1988. 25. 46. Smith, R . M., and Burr. C. M.. J . Chrornarogr., submitted for publication. Smith, R. M.. J . Chromarogr.. 1981, 209, 1 .ANALYTICAL PROCEEDINGS, JANUARY 1989, VOL 26 27 The Determination of Quantum Efficiencies of Laser Dye Using the Thermal Lens Effect Jun Shen and Richard D.Snook Department of Instrumentation and Analytical Science, UMIST, Manchester M60 1 OD The absolute fluorescence quantum efficiency of fluorescence materials is an important parameter for both fundamental theory and analytical applications. It is important for the study of radiation processes in molecules. 1 for correlation of predic- ted luminescence lifetimes with the observed lifetimes2 and for making assignments of electronic transitions.' It is necessary for calculating thresholds for laser action4 and for judging the suitability of materials as wavelength shifters in optical pumping experiments or for use as energy donors.' With luminescence data, it is also used to evaluate the purity of a material. 1 Although the absolute quantum efficiency is of great importance, measuring this parameter precisely is never easy.In the past, many measurement techniques have been devel- oped, including radiation integration methods, fluorescence lifetime methods, calorimetry, etc. However, all these tech- niques require absolute calibration for the optical detectors. Luminescence standard samples whose fluorescence quantum efficiencies are exactly known are also required. The accuracy attainable with very careful experimental procedure is typically 5-10%. When substantial corrections for different conditions, such as solvents, are invoked or when instrumental sensitivity at widely differing wavelengths must be considered, total uncertainties can easily reach 25%. In addition, the number of the absolute primary standards is extremely small.Consequently, the measurement becomes quite complicated. The measurement of absolute quantum efficiency using the thermal lens effect was first pointed out by Hu and Whinnerys and applied to liquid solution by Brannon and Magde.6 Unlike conventional quantum efficiency measurements, this method is absolute and does not need any luminescence standard and significantly reduces uncertainties. It could, therefore, become a standard laboratory technique for measuring quantum efficiency. Sodium fluorescein is probably the second best characterised luminescence standard after quinine sulphate in 0.1 or 1.0 N sulphuric acid. However, the quantum efficiency values of sodium fluorescein are still not accurately determined, lying between 0.77 and 0.95.This project concerns, therefore, the determination of absolute fluorescence quantum efficiencies of the laser dye sodium fluorescein in 0.1 N aqueous sodium hydroxide and in ethanol, using the thermal lens effect. Development and Detection of the Thermal Lens Thermal lensing was first reported and discussed in detail by Gordon et al.7 and was used to measure the absorption coefficients of liquids. The most important advance in the thermal lens technique was introduced by Hu and Whinnery.' The single-beam thermal lens experimental set up is quite simple (Fig. 1). A liquid sample is placed in the beam of the laser and is heated by the absorbed laser power. The heat dissipated to the solution creates a temperature gradient which Laser Shutter Cell Pinhole I I ~ P M T Filter Lens -1- r\ ,I u1 u2 u 3 Fig.1. Single-beam thermal lens experimental set up. D,, focal length of lens; Dz. confocal length; D3. arbitrary produces a refractive index gradient, thus creating an effective optical lens. As most liquids have a positive coefficient of thermal expansion. the temperature coefficient of the index of refraction, dnldt, is negative, and the thermal lens is divergent. When a Gaussian profile laser beam is passed through the liquid at t = 0, an effective lens develops in the liquid according to7 x k w 2 F(t) = (1 + t,./2r) . . . . (1) Pth(dn/d r ) Here F(t) is the focal length of the thermal lens (cm); k is the thermal conductivity (W cm-1 K-1); w is the radius of beam in the liquid (cm); 1,- wzpcl4k and is the critical time, where p = density (g cm-3) and c = specific heat (J g-1 K-I); P t h , the thermal (heat) power, is the incident laser power (W) which is absorbed and converted to heat; dnldt is the refractive index change with temperature (K-I).For a single-beam thermal lens experiment, the thermal lens in the sample is detected by its effect on the propagation of the laser beam. The magnitude of the thermal lens signal can be monitored by measuring the laser intensity at the beam centre, which is inversely proportional to the beam area in the target pinhole. If the sample is placed at the confocal length, past the focus, the maximum de-focusing effect on the laser beam will be exhibited. Here, the confocal length b = n wC12/h where h is the laser wavelength (cm), w ( ~ is the beam waist radius (cm).The expression relating the intensity Z(t) as a function of time is given as5 z(t) = z ( ~ ) [ i - e/(i + t,/2r) + fe2(i + tJ2t)I-l . . (2) . . . . . . ( 3 ) Pth(dn/dT) h k e = 8 and thus the thermal (heat) power can be determined by measuring the initial intensity Z(o) and the intensity after steady state has been established I(=). That is . * (4) e = 1 - (1 + 21)1 I = [ I = [Z(o) - I( q l I ( = ) . . Determination of Absolute Quantum Efficiency by Thermal Lens The laser power, P , incident on a sample is equal to the sum of transmitted power P,, the fluorescence emission power P f , and the thermal (heat) power f t h (Fig. 2). P = f , + f f + f , h . . . . . . ( 5 ) A Fig. 2. power; Pf fluorescence emission power; Prh thermal (heat) power Power conservation.P is incident laser power; P, transmitter28 ANALYTICAL PROCEEDINGS. JANUARY 1989. VOL 26 The transmission defined as: So the absorption ratio T and absorption coefficient A are T = P,/P . . . . . . . * (6) A = l - T . . . . . . . . (7) AP=Pf+Pth . . . . . . (8) power is The definition of fluorescence efficiency, Qf, is Number of photons emitted Qf = Number of photons absorbed That is (9) Here, ( v v ) and ( A f ) are the average huorescence frequency and wavelength; v and h are incident laser frequency and wavelength. (A,) can be obtained from the fluorescence spectrum E(h) of the sample. (A,) = / E ( h ) d h / \ y d h . . . . (10) The ratio (hf)/h takes Jaccount '6f the Stokes shift. The absorption coefficient, A , may be measured with an ordinary spectrophotometer and the thermal (heat) power can be measured using the thermal lens effect.In addition to measuring the sample, a measurement of a non-fluorescence absorber, designated by a superscript r, is made. We have From ( 3 ) , (4), (9) and (11) we have Q - , - (A,) - [ I--- A r f r p t h ] . . . . h A P P:h If the dilute solutions are used in the experiment, and the same solvent is used for both sample and reference absorber, then L 3 Equation (13) assumes that the laser wavelength is the same and that the optical properties of the solution are dominated by the solute, and the thermal optical properties of the solution are solely determined by the solvent. Experiment Fig. 1 shows a single-beam lens experiment set up. The laser was an argon ion laser (CR-6 Supergraphite Ion Laser, Coherent) operating at 488 nm.The laser is focused by a lens with a focal length of 20 cm with a mechanical shutter placed at the focal plane. A sample cell is placed at a distance of about 23 cm from the lens. The exact position is optimised by seeking the location which maximises the thermal lens effect. This has been shown to occur at the confocal distance past the focus.5 A photomultiplier tube with a pinhole (aperture = 2 mm) is located 3.5 m from the sample and is positioned accurately at the centre of the laser beam. Although a relatively large pinhole, the aperture of 2 mm radifis was much smaller than the far-field radius of the beam (3 cm), thus averaging out high frequency spatial noise from surface imperfections in the optical components.An inconel coated neutral density filter was placed very close to the pinhole in order to minimise the effect of stray light on the PMT. The output of the PMT was d.c. coupled to a storage oscilloscope (Tektronix 466). The photometric absorption measurements were made with an ultraviolet - visible spectrophotometer (Lambda 5. Perkin- Elmer). The fluorescence spectra of the samples were obtained from a luminescence spectrometer (LS-5, Perkin-Elmer). Solutions were contained in 1-cm fused silica cells, and the same cells were used for both photometric and thermal lens measurements. The sample, sodium fluorescein, and the reference absorber, pararosaniline, were obtained from the Sigma Chemical Company Limited. According to the assay data obtained from Sigma, no impurities in the sodium fluorescein were detected.The solvents were 0.1 N aqueous sodium hydroxide and ethanol. We noticed that several experimental constraints are imposed on the method in the derivation of Equations 1 4 : firstly, the laser beam must have a TEMoo Gaussian profile; secondly, the thermal (heat) power must be low enough to avoid spherical aberrations and convection effects, which requires Pth C2.2 h k/(dnldt); thirdly, the sample cell should be accurately positioned at a confocal length past the focal plane; fourthly, the sample cell length should be long compared with the beam diameter to avoid end effects; fifthly, the sample cell should be short compared with the confocal distance to ensure uniform beam area throughout the sample; and sixthly, the aperture of the pinhole must be small with respect to the far-field beam area and accurately centred. Water is not a sensitive solvent for the effect because of its large thermal conductivity and small drzldr. However, its use as a solvent was investigated. About 20 mW laser power was used to do the experiment when using water as a solvent compared with 10 mW laser power to measure the quantum yield when using ethanol as a solvent. For ethanol a blank correction was required, because f t h is additive for both sample and refer- ence. 0 = 0 (solution) - 8 (solvent) . . . . (14) In the experiments the shutter was opened for about 1.5 s at intervals of about 3 min so that the sample could relax sufficiently in the intervals. Solutions were freshly prepared and the measurements were taken at room temperature. The results of the measurements are shown in Table 1. being the average of twelve signals each. Results By using the data in Table 1. together with the Stokes factor. we obtained the absolute quantum efficiencies of sodium fluorescein in 0.1 N sodium hydroxide solution and ethanol, Qt = 0.95 2 0.02 and Qf = 0.97 k 0.02, respectively. Literature values for sodium fluorescein in 0.1 N NaOH lie in the range 0.77-0.95. Demas and Crosby suggested8 that Q, = 0.90 is a compromise value which is accurate within 10% and probably within 5 % . Our result agrees with it perfectly and is repro- ducible. It is noticed that quantum efficiencies in ethanol are a little higher than those in 0.1 N NaOH, and that the average emission wavelength is a little lower than literature values. These differences are probably the results of trace impurities in the solvent. Table 1. Comparison of sodium hydroxide and ethanol solvents Dye Solvent concentration (A,)inrn BiP W:P A Ar Pr 0.1 N NaOH l.0Ox 10-6 521.0 (5.95 t 0.48) (2.11 t 0.08) 0.120 0. I87 0.95 t 0.02 Ethanol l.0Ox 10 515.1 (1.30 k 0.20) 0.517 t 0.006 0.014 0.067 0.97 k 0.02 x 10-4 x 10-2 x10ANALYTICAL PROCEEDINGS. JANUARY 1989. VOL 26 The experiments have shown that the technique using the thermal lens effect is accurate, convenient to carry out, and does not require standardisation. It is also simple. inexpensive, and should become a viable technique for the measurement of absolute quantum efficiencies. References 1. Parker. C. A. “Photolurninescence of Solutions.” Elsevier Publishing Company. New York. NY. 1968. 29 2. Strickler, S. J . , and Berg. R. A . , J. Chem. Phys., 1962. 37.814. 3. Lytle, F. E., and Hercules, D. M.. J. Am. Chem. SOC.. 1969.91. 253. 4. Soroking, P. P.. Lankard, J . R., Moruzzi, V. L . , and Harnrnond, E. C.. J. Chem. Phys.. 1968,48. 3726. 5. Hu, C., and Whinnery, J . R., Appl. Opt.. 1973. 12. 72. 6. Brannon, J . H.. and Magde. D.. J. Phys. Chem., 1978,82,705. 7 . Gordon, J . P., Leite. R. C . C., Moore. R . S., Porto, S . P. S . . and Whinnery. J . R.. J. Appl. Phys., 1965, 36, 3. 8. Denas, J . N.. and Crosby, G. A.. J. Phys. Chem.. 1971,75.991.

ISSN:0144-557X    

DOI:10.1039/AP9892600016

出版商:RSC    

年代:1989

数据来源: RSC

摘要:

ANALYTICAL PROCEEDINGS. JANUARY 1989. VOL 26 29 Analysis of Sodium in Blood Plasma Using a New Mini Ion-selective Electrode Martin Telting-Diaz, Malcolm R. Smyth and Dermot Diamond* School of Chemical Sciences, National Institute for Higher Education, Glasnevin, Dublin 9, Ireland Eileen M. Seward, Gyula Svehla and Anthony M. McKervey Department of Chemistry, University College, Cork, Ireland The popularity of ion-selective electrodes is well recognised today. Numerous medical centres use them on a routine basis for the analysis of the most relevant physiological ions in clinical practice, e.g., Na+, K + , CaI+ and H+.l As regards sodium, the development of the sodium glass membrane has permitted the potentiometric analysis of various body fluids: whole blood,? serum,3.4 plasma2.5 and urine.z.4.h Today much modern equipment uses this analytical method for sodium measurements in clinical laboratories.The advantages of the electrodes are well catalogued in the literature.7 in particular when they are compared with more sophisticated methods of sodium analysis, such as flame photometry or atomic absorption. PVC sodium selective membranes based on neutral carriers have not yet achieved the popularity of the glass membrane, even though it is well known that the performance of electrodes based of these membranes is superior to that of the glass electrode in terms of lower membrane resistance, lack of contamination by proteins depositing on the membrane surface, the obvious easy construction. general robustness and the possibility of implanting micro-PVC electrodes into the human body.Derivatives of calix(.l]arenes have shown an ability to complex alkali metal ions.s.y X-ray crystallographic studies of some of these macrocyclic compounds have established a cuplike configuration, with polar groups facing towards the cavity. and ordered in such a way as to promote ion binding.]" The cavity of the ligand used in this research (methyl p-tert-butylcalix[.l]aryl acetate) (Fig. 1) is formed from polar phenolate and ester oxygen atoms.' I When incorporated into plasticised PVC membranes. a surrounding highly lipophilic layer ensures a good compatibility with the non-polar PVC plasticiser . Electrodes based on such ion-sensitive membranes have been found to respond to variations in ion activity in a Nernstian manner. i.e., E = E" + S log u, where a, are primary ion activities in sample solution; E is the measured potential: E" is the standard potential: and S is the Nernst slope factor.i.e., 2.303 RT/z,F, in which R is the gas constant. T the absolute temperature. 2 , the charge on the primary ion and F the Faraday constant. Ideally. a selective ionophort contained in a liquid or PVC membrane draws only one type of cation [the primary ion (i)] Author to whom correspondence 4hould be addressed. into the membrane phase. In reality, all ion-selective elec- trodes respond to cations other than the primary ion. The effect of these interfering ions 0) on the membrane potential is given by the Nikolski - Eisenman equation: E = E" + s log [a;+ T' a;,='] where all the symbols have their conventional meaning.12 Experimental methods for estimating selectivity coefficients have been outlined by Moody and Thomas.13 Fig.1. The ionophore methyl p-tert-butylcalix[j]aryl acetate (ligand 1C) showing the cone conformation with a separation between adjacent phenolic oxygen atoms of 0.3 1-0.33 nrnl' (oxygen atoms filled circles) Materials and Methods Chemicals and Samples All of the electrolyte solutions were prepared in Milli-Q water and the salts were of analytical-reagent grade. The calibration solutions and those used to determine selectivity coefficients for the separate-solution method were made up by serial dilution of 0.1 M stock salt solution.ANALYTICAL PROCEEDINGS, JANUARY 1989. VOL 26 The synthesis of the calixarene ester has been described earlier. 1 1 Plasticiser-mediator 2-nitrophenyl octyl ether (2- nPOE), potassium tetra-p-chlorophenylborate (KTpCIPB), poly(viny1 chloride) (PVC) and tetrahydrofuran (THF) were obtained from Fluka AG.while salts of Tris buffer were obtained from Sigma. The plasma samples were collected at St. James Hospital, Dublin. The samples had previously been analysed by means of a sodium glass electrode using the Technicon method,lj which involves dilution of the sample six times before it is screened. One aliquot of each sample was taken and adjusted to pH 7.4 with Tris buffer. The samples were then diluted ten times. The composition of the membrane cocktail used throughout this research is given in Table 1. Table 1. Membrane cocktail composition Component O/o m/m Ligand 1C 1.3 2-nPOE 65.0 KTpClPB 0.3 PVC 33.3 Electrodes and Instruments Electrodes were constructed by introducing a chloridised silver wire (Johnson Matthey Ltd.) into a 1 mm i.d.PVC tube (EMS Medical Group Ltd., Stonehouse, Gloucestershire) about 16 cm long. One end of the wire was soldered to a 2 mm plug, which was subsequently fixed to the tube by glueing with an epoxy adhesive. At the other end, the wire was cut to size and a 4 5 mm porcelain tip (Morgan Matroc Products Ltd.). glued in place with a drop of tetrahydrofuran (Fig. 2). To coat the PVC membrane on to the porcelain, the tip was submerged several times in the membrane "cocktail" and left to dry by evaporat- ing the THF for 24 h at room temperature. The electrode was C d e Fig. 2.Schematic representation of a PVC mini-ion-selective elec- trode: ( a ) , chloridised silver wire; ( b ) . PVC electrode body ( 1 mm i.d.); ( c ) , internal reference electrolyte (0.1 M NaCI); ( d ) , ion sensitive PVC membrane; (e), porcelain tip; ( f ) . 2 mm electrical DIUE next filled with the internal solution (0.1 M sodium chloride) by injecting it with a fine syringe into the PVC tube body. The electrode was then left to condition in 0.1 M sodium solution for 1 h prior to use. The indicator electrodes constructed were used with a Metrohm AG 9100 Herisan reference electrode, connected to a Philips PW 9421 digital pH/mV meter and a Linseis 16512 chart recorder. The meter was standardised and used according to the recommendations of the manufacturer. The e.m.f.measurements were carried out on cells of the type: Hg, Hg2C12/KCl(satd)/ Reference Sample/ PVC membrane/O. 1 M NaCVAgC1,Ag ISE Selectivity Coefficients and Electrode Function To determine the slope of the electrodes, potentials were measured in six standard solutions of NaCl over the range 10-'-10-6 mol 1 - 1 . The response to a number of possible interfering ions over the same range is shown for comparison in Fig. 3. Selectivity coefficients wi (tabulated in Table 2) were obtained by the separate-solution method," using the expres- sion E,-E, = log KF;"' 2.303 RTIF where E, and E j are the potentials measured in solutions of the various interfering ions (j) and the primary ion (i) at equal activities (0.1 M). Corrections for experimental e.m.f. values were made for estimated variations in liquid junction potential using the Henderson formula.15 The activity coefficients were calculated on the basis of the Debye - Huckel formalism.li Table 2. Comparison of selectivity coefficients and slopes for a variet!, of sodium ion selective electrodes. See reference 4 for glass membrane electrode Selectivity coefficients (log Kilo') Mini-electrode* based on Ion ligand 1C Cs + H i K+ NH' + Li + Mg'+ SlopeimV Ca2 t -1.51 -1.88 -2.47 -2.74 -2.78 -3.12 -3.74 58.1 f 0.8 ETH 227 -2.24 -0.1 0.0 -1.7 0.5 -1.5 57.5 k 0 . 1 - 3 3 &.A Glass ETH 157 electrode - 1 .5+ -3.0 0.7 3 . 0 -0.4 -3.0 - 1 .O+ -4.5 -1.7 -3.0 -3.3 - -3.1 - 60.1 k 0.7 * Determinations obtained by the separate-solution method by using 0.1 M solutions. The values for the membranes denoted as ETH 227 and ETH 157 have been obtained by Simon and co-workers' and correspond to two different Na + ionophores. + Values obtained with macro-electrode.Procedures For studies involving determinations of selectivity coefficients, sets of up to 10 electrodes were assayed and the electrode that presented less drift was selected to perform the analysis. The e.m.f. values used for calculations were the mean of the potential measured at 10 and 15 min after immersing the electrodes in the sample. The measurements were performed at 20 + 1 "C throughout.ANALYTICAL PROCEEDINGS. JANUARY 1989. VOL 26 - E 140 m cs i, 130 B 31 ' 1 I I /+ Na- i 1 J Log activity Fig. 3. Calibration curves for important cations obtained ivith mini-ion-selective electrode based on ligand 1 C.Solutions range from 10 f1 to 10- I 51 (all CI salts except MgSO,) -6 -5 -4 - 3 -2 -1 0 In order to determine the e.m.f. of plasma samples. six sodium calibration solutions were made up and the slope of the electrode function calculated before attempting any measure- ment. These stock solutions contained 50.0. 125.0. 130.0. 155.0, 200.0 and 500.0 mmol 1 - 1 of Na+ with a constant ion background of K+ (4.0 mmol 1 - 1 ) . Caz+ (1.1 mmol 1-1) and Mg'+ (0.6 mmol l-I). When taking measurements. 1 ml of each stock solution was removed, 2 ml of Tris buffer added (pH 7.4) and the volume made up to 10 ml. A similar procedure was used with blood samples, i.e., 2 ml of Tris buffer (pH 7.4) were added to 1 ml of blood plasma and the total volume made up to 10 ml.To obtain the plasma, the blood samples were centrifuged at 3500 rev min-1 for 10 min. After every third or fourth sample the electrode response was checked in the calibration solutions. Two electrodes were used to analyse a total number of 44 plasma samples (see Results and Discussion). Results and Discussion PVC sodium mini-ion-selective electrodes have been construc- ted by using methyl p-tert-butylcalix[4]aryl acetate as iono- phore for the application of sodium analysis in blood plasma. The values obtained for selectivity coefficients were reprodu- cible and found to agree well with those obtained in earlier studies for the same ionophore.16 The pattern of selectivity against interferents shown in Fig. 3 is broadly similar to that 160, 1 2 0 ' + L 120 130 140 150 Glass electrode: C,; :mmol I ' 160 Fig.4. Correlation between t\vo indirect potentiometric methods for the measurement of sodium concentration in 24 plasma samples. The slope of the electrode is 58.1 k 0.8. Smac Analyser (sodium glass electrode). sample diluted six times: mini-electrode (based on ligand 1C). sample diluted ten times. The ideal correlation between both wts of results is shown by the segmented line obtained by phase-transfer studies. 1 1 The comparison shown in Table 2 includes two PVC membranes which are currently available, and the traditional glass membrane. Ligand 1C exhibits better selectivity towards K+ and Li+ than ETH 227 and ETH 157, and a similar sensitivity towards these ions compared with the glass membrane. Ligand 1C presents the best selectivity against H+ ions.Fig. 4 shows results obtained with mini-ISE's in 24 plasma samples compared with the Technicon method. Although a good correlation was obtained (coefficient = 0.94) a small but systematic error was evident (3.1 mmol 1 - 1 average). A second batch of 20 plasma samples showed a similar pattern (Fig. 5 ) with a good correlation (coefficient = 0.95) but with a constant slightly negative error in this instance (4.6 mmol 1 - 1 average). The origin of the systematic error is at present unknown but could arise from differences in the hospital or our own calibration procedures. - - 150 r------------l / /' + 120 ' I 120 130 140 150 160 Glass electrode: CNa+ immol I - l Fig. 5. Correlation of sodium measurements in 20 diluted plasma samples. Other details as for Fig.1. The slope of the electrode obtained prior to measurements is 54.5 ? 0.3 At this stage the error is being investigated by comparing new sets of results with a reference photometric method. As more precision and reproducibility in the technique is desir- able, further work will involve using the electrodes in a flow injection system. 1. 3. 4. 3. 6 . 7. 8 . 9. 10. 11. 13,. 13. 14. 15. 1 &. 16. References Arnold. M. A , . and Solsky. R . L.. And. Chem., 1986.58. X4R. Ladenson, J . H.. Chi. Chern., 1979. 25. 757. Langloff. E . . and S e i n e s . I . , Clin. Chem., 1982. 28. 170. Anker, P.. Jenny. H. B.. Wuthier. U . . Asper. R . . Ammann. D.. and Simon. W . . Clin. Chern., 1983. 298. 1508. Preusse, C . J . , and Fuchs.C., J . Cliri. Chern. Clin. Hiochern.. 1979. 17. 639. Graves, S . W.. Koch. D. D . . and Ladenson. J . H.. Clin. Cliern., 1982. 28. 1631. Ladenson. J . H.. Anal. Proc.. 1983. 20. 554. Chang. Suk-Kyu. and Cho. Iwhan. J . Chem. Soc. Perkin Trutis. I , 1986. 2 1 1. Ferguson. G., Kaitner. B.. McKervey, M. A , . and Seward. E . M.. J. Chem. Soc. Chern. Commun., 1987. 584. Edmonds. T. E . . "Chemical Sensors." Blackie. Glasgow and London. 1988. pp. 17-69. McKervey. M. A . . Seward. E. M.. Ferguson, G . . Ruhl. B . . and Harris. S . J.. J . Chem. Soc. Cherii. Commun., 1985, 388. Ammann. D.. Morf. W. E.. Anker. P . . Meier, P. C.. Pretsch. C.. and Simon. W . . loti Selecri1.e Electrode Rev., 1983. 5 . I . Moody. G . J.. and Thomas. J . D. K.. "Selective Ion-Sensitive Electrodes," Merrow.Watford. 1971. " S MAC Tech n icon Me t hod . '* Tech n icon I n s t r u me n t s Co rpo r - ation. Tarrytown, New York. USA. Meier. P. C.. Ammann. D.. Morf, W. E.. and Simon. W., in Koryta. J . , Editor. "Medical and Biological Applications of Electrochemical Devices. John Wiley. Chichester. 1980. p. 13. Diamond. D.. Svehla. G.. Seward. E. M., and McKervey. M. A . . A n d . Chirn. Actn. 19x8. 204, 223.32 ANALYTICAL PROCEEDINGS. JANUARY 1989, VOL 26 A Semi-continuous Flow Method for the Trace Analysis of Dissolved Inorganic Antimony A. T. Campbell and A. G. Howard Chemistry Department, The University, Southampton SO9 5NH Antimony is found in most unpolluted natural waters at concentrations which are normally below 300 ng 1-1, a level at which there are comparatively few suitable analytical methods.Methods based on hydride generation AAS offer the required sensitivity and the opportunity of providing some degree of information on speciation. There are two main approaches to such methods. The large volume “batch” approach, in which the reaction is carried out in a chamber (e.g.. the methods of Andreae et a/.‘ and Apte and Howard*) and the continuous flow hydride generation methods that are constructed from automated analysis components (e.g., the methods of Goulden and Brooksbank,’ Schmidt et al. ,4 Arbab-Zavar and Howard’ and Yamamoto et al.6). The detection limits of these methods can be improved by using a variety of collection procedures prior to transfer to the atomiser; these include balloons, pressurised chambers.collec- tor solutions and cryogenic traps (see reviews by Godden and Thomerson7 and Nakaharas). The lowest concentration detec- tion limits are generally obtained by using batch generation methods from large sample volumes and pre-concentration of the analyte. Such methods are, however, time consuming and involve much manual manipulation. and this results in a comparatively low sample throughput. Continuous flow methods, on the other hand, generally have better reproduci- bility and more rapid sample throughput, but, having no analyte pre-concentration step, lack the required sensitivity that would be required for the analysis of dissolved inorganic antimony in uncontaminated natural waters. The system to be described is a development of a technique that we have used for some years for the speciation of arsenic (Arbab-Zavar and Howardy and AptelO).This paper sum- marises the chemical and system parameters required to permit the method to be capable of the analysis of dissolved antimony in natural waters at the ng 1 - 1 level. Experimental Reagents All of the reagents used were of analytical grade unless otherwise stated. Glassware and plasticware were cleaned by overnight soaking in 1Ooh V/V hydrochloric acid followed by rinsing with distilled water. Stock standard solutions contain- ing 100 mg 1-1 of antimony(II1) and 250 mg 1-1 of antimony(V) were prepared from potassium antimony1 tartrate and potas- sium antimonate (laboratory-reagent grade). respectively. in 10% V/V hydrochloric acid.These were cross-calibrated by using flame atomic absorption spectrometry. Lower concentra- tion standards were prepared by dilution on the day of use. Sodium terrahydroborate. Laboratory-reagent grade material was dissolved in distilled water to give an unstabilised solution (2% mlV). The sodium tetrahydroborate has a significant antimony blank but can be purified by the slow addition of 2 cm3 of hydrochloric acid (1 + 9). whilst bubbling nitrogen through the solution. Potassium iodide. Potassium iodide was used to prepare a 1 M solution. This was stabilised by the addition of 2.4 g 1-1 sodium hydroxide solution and stored at 4 “C in a brown-glass bottle. Sulphanilantide solution (0.1 M ) . This solution was prepared in hydrochloric acid (1 + 9). A pH 5.0 buffer was prepared from sodium acetate solution (0.1 M ) , adjusted to the required pH with glacial acetic acid.Apparatus The apparatus consists of three distinct stages (Fig. 1). Continuous flow hydride generation is carried out by using a peristaltic pump with four reagent lines, a fourteen turn delay coil and a gas-liquid separator. In the top of the separator sodium hydroxide pellets act as a water trap. Gaseous products are then swept from the separator into a cryogenic trap containing 40-mesh hydrofluoric acid etched glass beads packed in a borosilicate glass U-tube. Detection of stibine is carried out by atomisation in an electrothermally heated quartz T-tube suspended in the light path of a Varian Techtron AA5 atomic absorption spectrometer. Air -1 ?= d trap I Waste Fig.1. The semi-continuous-flow apparatus for the determination of antimony by hydride generation AAS In the continuous flow hydride generation system the sample is acidified, segmented with air and then reacted with sodium tetrahydroborate. The products are then swept through the delay coil and stripped from solution in the gas-liquid separator. The stibine is then condensed at -196 “C in the U-trap. After trapping, the liquid nitrogen is removed and the i: Blank Time - Fig. 2. Typical output from the hydride systemANALYTICAL PROCEEDINGS. JANUARY 1989, VOL 26 trap allowed to warm to room temperature. This results in the release of the stibine to the atomisation - detection system (Fig. 91 33 i). Determination of Total Antimony A 5-cm-3 aliquot of the sample is pipetted into a glass sample cup, and 0.5 cm-3 potassium iodide (1 M ) pre-reductant is added, together with any masking reagents.The U-trap is cooled with liquid nitrogen and the peristaltic pump started. The sample probe is then placed in the cup and the sample is taken up over a period of 2.5 min. Pumping is continued for a further 1.5 min to ensure complete trans- mission of the stibine to the trap. The liquid nitrogen is then removed and the trap allowed to warm, resulting in the elution of stibine into the quartz tube atomiser. The resultant spectrometer output is recorded on a Y-r chart recorder (Te kman TE200). Determination of Antimony(II1) Antimony( 111) can be selectively determined using the above system by replacing the hydrochloric acid with a sodium - acetic acid buffer adjusted to pH 5.0.Table 1 . Spectrometer conditions Source Lamp current Wavelength Spectral band pass Furnace temperature Chart speed Chart sensitivity Antimony hollow cathode lamp 6 mA 217.6 nm 0.33 nm 900- 1000 "C 30 mm min- I 10 mV fsd Results and Discussion Optimisation The above procedures were optimised by using a univariate approach, which gave the conditions shown in Tables 1 and 2. Table 2. Optimum systeni parameters Hydrochloric acid 1 + 9 2% mlV Sodium tetrahydroborate Nitrogen gas flow-rate 250 cm3 min I Potassium iodide 0.5 cm3 ( 1 M) S u I p ha n i I am i d e 0.4 cm3 (0.1 M) * Adjusted to pH 5.0 by use of concentrated acetic acid. Sodium acetate 0 . 1 M* ~~ Interferences Potential interferences were studied by the addition of a known amount of foreign ion to a sample.Table 3 shows that both the total antimony and antimony( 111) systems suffered from a number of interferences. In general, however, the concentra- tions tested were far in excess of their natural occurrence in estuarine water and seawater. The main exception to this was nitrite. which interfered down to a concentration of 100 mg 1 - 1 in both systems. This interference was overcome by the addition of 400 pl of sulphanilamide (0.1 M ) to the sample prior to analysis. With the transition metal interferences, all except copper were removed by adding 300 ul of EDTA (0.002 M ) to the sample." In the instance of copper, this interference was removed by using 300 u1 of 1,10-phenanthroline (0.015 M ) . Speciation Species selectivity was obtained by careful control of the pH of the reaction.By using the sodium acetate-acetic acid buffer system antimony( 111) was selectively detected in the presence of a ten-fold excess of antimony(V). Hence. speciation information could be obtained by subtracting the concentra- tion of antimony(II1) obtained on one aliquot of a sample from the total antimony concentration obtained on a second aliquot. Table 4 shows the performance data for the system. It illustrates that the method is well suited to antimony speciation studies in the ng 1 - 1 concentration range. Even at the levels that can be determined with this method, the technique is still not suitable for the determination of antimony(II1) in unpol- luted natural water samples. It is, however, capable of providing useful information on the levels of total dissolved inorganic antimony in natural waters and may also be applicable to the analysis of sediment and tissue digests.interstitial water and industrial effluents. Table 3. Interferences Concentration of interferentimg I I 10 Antimony( 111) Pb' + (32";)' Fe'- (100%) NC+( l0Oo%) Co?+(74%,) Cr" - ( 86(!& ) Hg + (94% ) Cd'+ (100%) Mn'* (IOO'X)) Bi3-(42(Yl) Br (33%) Coz- (8%)Cr~~+(I6(%) CU"( 100°i,) Fe'+ (IOOYo) NO:-( lOO'l'o) A n t i m o n y (total) Hg ~ ( 7 . 3 % ) CU" (IOO'?") Fc"(8"4) NO?- (lOO?//;) * Percentages represent signal suppression. Table 4. Figures of merit Linear rangelng Preci 4 o n Detection limits (1 cm') ( 3 x s . d . o f h l a n k ) (5cm') Sample rate ( 1 cm3) ( 5 cm') 1 cm' 5 cm3 * I I = Number of replicates.34 ANALYTICAL PROCEEDINGS, JANUARY 1989.VOL 76 References 1 . 2. 3. 4. Andreae. M. 0.. Asmode. J . F.. Foster. P.. and Van" Dack. L.. Atiul. Chetn., 1981. 53, 1766. Apte. S . C.. and Howard. A. G.. J . At. Ahmrp. Spectrosc.. 1986. 1. 221. Goulden. P. D.. and Brooksbank, P.. Anal. Chem., 1974. 46. 1431. Schmidt. F. J . . Roger, J . L., and Muir. S . M.. Atial. Lett., 1975. 8 . 123. 5 . Arbab-Zavar. M. H.. and Howard. A. G.. Am~!\~.st. 1980. 105. 744. 6. Yamamoto. M.. Yasuda. M., and Yamamoto. Y.. Atid. Chetn., 1985. 57. 1382. 7. Godden. R. G.. and Thomerson. D. R.. AtitiITst. 1980. 105. 1137. 8. Nakahara, T.. Proj. Anal. Ar. Spectrosc., 1YX3. 6 . 103. 9. Howard. A. G.. and Arbab-Zavar. M. 14.. Atitr!\w. 1981. 106.213. 10. Apte. S . C.. PhD The5i.s. 1985. University of Southampton. The Capillary Gas Chromatography - Atomic Absorption Spectrometry of Organotin and Organolead Compounds R. C. Forster and A. G. Howard* Chemistry Department, The University, Southampton SO9 5NH The widespread use of organometallic compounds and their consequent release into the environment has lead to increasing concern over their persistence and toxicity. Organotins, and in particular tributyltin (TBT) compounds, have been widely used as biocides in marine anti-fouling paints and leaching from boat hulls results in the release of TBT into the coastal environment. Reduced shellfish numbers' have been linked to shell thickening in oysters'.' and imposex in dog whelksj; both of these conditions can result from exposure to TBT.As a result of the toxicity of TBT to non-target organisms legislation has been introduced to control the use of paints containing TBT. A level of 20 ng 1 - 1 has been proposed as a target for TBT in natural waters' but recent work would suggest that even this may be too high.6 Organolead compounds have found their major application as anti-knock agents in petrol. The release of lead into the environment occurs as both inorganic salts and as the more toxic alkylleads. As with TBT, many countries have introduced legislation that is designed to phase out their use. If the impact of organometallic compounds on the environ- ment is to be assessed then speciation of the elements at environmental levels is necessary. This paper describes the construction and development of a capillary gas chromato- graph (GC) system for the determination of organometallic species.The system employs the excellent separating power of capillary gas chromatography with the selectivity of detection shown by atomic absorption spectrometry. Improved sensitiv- ity is obtained by using on-column injection of up to SO-pl aliquots of the sample extract. Experimental Instrumentation The apparatus consists of a Pye 104 gas chromatograph (GC) interfaced to an Instrumentation Laboratory Model 25 1 atomic absorption spectrometer. A resistively heated transit line is used to conduct the capillary column into a flame-in-tube atomisation cell aligned in the spectrometer light path. ~~~~ To whom correspondence should be addrefsed.Gas Chromatography Chromatography was carried out on a 0.3 mm i.d., 10 m quartz capillary column coated with an immobilised methylsilicone stationary phase (1 pm film thickness). The retention gap was 15 m of 0.32 mm i.d. trimethylchlorosilane treated capillary tubing. Nitrogen carrier gas was employed at a sub-optimal flow-rate of f3-7 ml min-I and injection was carried out by using a custom built on-column injector purged with 14 ml min-1 of nitrogen. The chromatograph was temperature programmed at the following rates: tin hydrides. 30 "C for 8 min then 20 "C min-1 to 200 "C; tetraalkyllead compounds, 30 "C for 9 min then 12 "C min-' to 120 "C. Atomic Spectroscopy The following operating conditions were employed: sources. hollow-cathode lamps operated at 5 mA; wavelength.286.3 nm (tin), 217.0 nm (lead); band pass. 0.50 nm (tin). 1.00 nm (lead). Atomisation Cell Design The flame-in tube atomiser consists of a 1 cm i.d. tube attached to the transit line using a Swagelok fitting which has been modified for the introduction of hydrogen. When employed. air is introduced opposite the capillary inlet. Several designs of atomisation cell have been investigated: firstly. a basic quartz T-tube, 14 cm long, without air introduction; secondly, a quartz T-tube, 14 cm long. with air introduction; thirdly. a short quartz atomisation cell (4 cm long); fourthly a waisted quartz tube, as in the third design, but with added 1.5 cm wide bore ends (2.2 cm i.d.) to maximise light throughput; fifthly, a very short atomisation cell (1.5 cm long); and sixthly, a Pyrex atomisation cell (4 cm long).Derivatisation of Butyltins Di- and tributyltin species were derivatised before GC by using a variation of the hydridisation method described by Matthias er 01.7 Standard solutions of the butyltin chlorides were prepared by adding between SO and SO0 pl of a 1 pg ml-1 mixed standard (in methanol) to 1 dm-3 of distilled water. One hundred microlitres of a 1 ug ml-l solution of tripropyltin chloride (in methanol) was added as an internal standard.ANALYTICAL PROCEEDINGS. JANUARY 1989. VOL 26 35 v) 8.5 + .- C ; 6.5 I 0 4.5 m' 2.5 0 v) c L [D - .- 0.5 1.5 Fig. 1. Tin response surface under varying air - hydrogen flow-rates 8.5 2 6.5 2 2 .- t 3 4- 4.5 g m - 2.5 2 0 v) 0.5 .- To the aqueous solution was added 10 ml of pentane, then 20 ml of 4% (mlV) aqueous sodium tetrahydroborate.The mixture was shaken for 2 min. then the upper pentane layer was separated and dried over anhydrous sodium sulphate. Finally, 80 yl of the extract was injected into the GC-AAS. Results and Discussion Atomisation Cell Design The burning characteristics of the tubes vary greatly. The basic T-tube gave rise to hydrogen flames burning at the ends; this was the least sensitive. Provision of air causes the flame to burn centrally, resulting in improved sensitivity; any excess hydrogen burns at the tube ends. but contributes little to the sensi t ivity . Table 1. Performance of the system. Detection limits based on 3 x standard deviation of the blank (17 = 3). Characteristic concentration = concentration required to give a peak height absorbance of 0.0044 RSD.(11 = 6) limiting O/" Detection Me,Pb* 5 0.28 Me,EtPb* 10 0.22 Me2Et,Pb 4 0.17 MeEt,Pb 4 0.19 Et,Pb 5 0.33 Detection lirnitipg I ~ 1 of lead 5.6 4.4 3.5 3.8 4.5 Characteristic concentration/ 17 31 17 17 20 pg 1 1 of lead RSD. Detection limit,' Characteristic ( n = 4) oftin of tin in water YI n g l - l concentration/ng 1 ~ I Bu2Sn* 4 15 130 BuSn 7 13 190 Bu,Sn 7 4 9( 1 * Me = methyl. Et = ethyl. Bu = n-butyl. I ( a ) ! DMDEL TEL TML TMEL I MTEL I 6 0.01 - e v) 0 5 10 15 Retention timeimin I 0 5 10 15 Retention timeimin Fig. 2. Example chromatogram obtained using the capillary GC - AAS system. (a). Organolead species (SO ul of a solution containing. in order 0 1 chromatographic elution. tetramethyllead.trimethylethyl- lead. dirnet hyldiethyllead. triethylmet h yllead and tetraethyllead ; approximately 2 ng of lead in each component injected. ( h ) . Organotin species its their hydrides (80 ul of an extract from water containing 500 ng I - 1 of tin as dibutyltindichloride. tripropyltinchloride. tributyltin- chloride and tetrabutyltin) With the exception of the very short tube. which gave poor sensitivity, there was little difference between the other types of tube showing minimal atom trapping. For much of the work reported here. a short Pyrex atomisation tube was therefore employed. This was easier to construct than the quartz tubes and, being short, gave the most straightforward alignment in the light beam. Gas Optimisation for Organotins With a 4 cm quartz atomiser fitted to the instrument.peak height sensitivity was measured by injecting 1 111 of a solution of tetraethyltin (20 ng of tin per microlitre) in pentane, under various flame gas stoicheiometries. From these data a response surface was constructed (Fig. 1 ) and optimum conditions were found to be 130 ml min-1 of hydrogen and 165 ml min-I of air (this was also found t o be the optimum for detection of alkyllead compounds).ANALYTICAL PROCEEDINGS. JANUARY 1989. VOL 26 Injection of Large Volumes The conventional injection of 1-p1 samples into a GC limits concentration based detection limits. Although as yet not widely used, the injection of large volumes on to capillary columns is possible. This can be achieved by using a custom designed on-column injector and a long retention gap.8 With a 15 m retention gap it has proved possible to inject volumes up to 80 p1 routinely, thereby significantly improving the sample based limits of detection. Performance Examples of the application of the apparatus to the determina- tion of organotin and organolead species are shown in Fig.2. The system preserves the chromatographic integrity of even the higher boiling components and no deterioration of chro- matographic performance is evident from the on-column injection of large volumes. The performance of the instrument is summarised in Table 1. Calibrations were linear up to 500 ng I-’. Conclusions The interfaced capillary GC - AAS system has proved to be a powerful tool for the analysis of organometallic species. It combines the excellent separating power of capillary gas chromatography with the selectivity of detection by atomic absorption spectrometry.Improvements in sample based detection limits have been shown to be possible by large volume on-column injection. The authors would like to thank the Trustees of the Analytical Trust Fund for the provision of an SAC studentship for the execution of this work. 1. 3 -. 3 . 3 . 5 . 6. 7. 8. References Alzieu, C., Heral, M., Thibaud, Y.. Dardignac. M. J., and Feuillet, M.. Rev. Trav. Inst. Pech. Marir., 1982, 45, 100. Waldock, M. J., and Thain, J. E., Mar. Pollur. Bull., 1986, 17. 542. Alzieu, C., Sanjuan. J., Deltreil. J. P.. and Borel. M.. Mar. Pollut. Bull., 1986, 17. 494. Bryan, G. W., Gibbs. P. E.. Hummerstone. L. G., and Burt. G. R., J . Mar. Biol. Assoc. U . K . , 1986, 66, 611. UK Department of the Environment Pollution Paper No. 25. .* 0 rg ano t i n in Anti - fo ul i n g Pain t s : E nv i ro n m c: n t a I Con si de ra - tions,” HM Stationery Office, July. 1986. Waldock, M. J.. Thain, J . E . . and Waite. M. E., Appl. Organomet. Chem., 1987. I , 287. Matthias, C. L.. Bellama, J. M., Olson. G. J., and Brinckman. F. E., Environ. Sci. Technol., 1986. 20, 609. Grob, K., Karrer. G . , and Riekkola, M.-L.. J . Chromarogr., 1985, 334, 129. THE ROYAL SOCIETY OF CHEMISTRY ANALYTICAL DIVISION EIGHTH SAC CONFERENCE-SAC 89 will be held at the University of Cambridge on July 30-August 5,1989 This Conference is organised by the Analytical Division of The Royal Society of Chemistry and sponsored by IUPAC and FECS. The scientific programme, which will be published in full in a forthcoming issue of Analytical Proceedings, will cover all aspects of analytical chemistry; there will be workshops and update courses and an attractive selection of social events for delegates and their guests. Details of the Conference and registration forms can be obtained by application to the Secretary of the Analytical Division, The Royal Society of Chemistry, Burlington House, Piccadilly, London W1V OBN.

ISSN:0144-557X    

DOI:10.1039/AP9892600029

出版商:RSC    

年代:1989

数据来源: RSC

摘要:

ANALYTICAL PROCEEDINGS, JANUARY 1989, VOL 26 37 Electron Spin Resonance Spectrometers The RE Series of ESR spectrometers are designed for ultra-high sensitivities and long term stability. With sensitivities of 1010 spid0.l mT, they can provide a wealth of information in materials science, biological, geological, phar- maceutical, food and semiconductor research. Biological studies cover photo- synthesis, enzyme reactions, drug detec- tion and radiation damage. In medicine ESR can be used to investigate carci- nogenic reactions, intact cells and radicals in tissues. The RE Series instruments feature a solid oscillation element, a Gunn diode, as the microwave power source; its durability is 20000 h or more. A signal to noise ratio of 460: 1 is achieved. A choice of magnets is offered with pole diameters of 150, 180 and 300 mm.Options include cavities for high and low temperature working, for light irrad- iation, wafer measurement and light detection. Extensions are available for ENDOR experiments, spin-echo, rapid scan and Q-band operation. Jeol UK Ltd., Jeol House, Grove Park, Colindale, London NW9 OJN. X-ray Fluorescence Equipment A new detector for energy-dispersive X-ray fluorescence work uses a new design of field-effect transistor which permits a performance level approaching the theoretical resolution of solid-state detectors. It has a peak-shape perfor- mance FWHM to FWHM of 1.89: 1, a peak-to-background performance of 10 000 : 1 and an exceptionally high count rate performance. Also available are the XZ8 thin-window detector and X-ray tube kit, which allow the makers’ EDXRF spectrometers to analyse elements as low as 0 ( X = 8), as well as providing improved detection limits for other low- energy elements.For example, the XZ8 reduces the limit by five times for sodium and permits a detection limit below 100 p.p.m. for magnesium. Other products available include the LGEM detector, which is of particular importance in the newer high-energy transmission electron microscopes and in XRF analysis, and a small dedicated sample holder which reduces scattered background radiation in XRF analysis. Link Analytical, High Wycornbe, Buckinghamshire . HPLC Column The Asahipak ODP-50 high efficiency polymeric column from Asahi Chemical Industry Company of Japan contains a CIS modified polymer said to combine the best characteristics of silica with those of a polystyrene gel.As well as offering effi- cient separation of basic substances, ODP-50 provides sharp resolution of pep- tides, proteins, amino acids and vitamins. It equals reversed phase silica columns in separation efficiency with organic sol- vents. Unlike silica, however, it also gives the same performance with buffered and alkaline solutions. It has a pH range of 2-13. The column is available in two sizes: 15 cm x 4.6 mm and 15 cm x 6.0 mm. Particle size is 5 pm and NTP values exceed 7000. May and Baker Ltd., Liverpool Road, Eccles, Manchester M30 7RT. HPLC Packing Material Developed by the makers in association with the Wolfson Liquid Chromato- graphy Unit at Edinburgh University, Hypercarb is a porous spherical graphi- tised carbon packing, supplied packed into black high-efficiency columns which provide total reproducibility.Hypercarb columns exploit all the theoretical advan- tages of porous graphitised carbon, notably the truly uniform surface and high mechanical strength. It has the robustness of ODS bonded silica gels but it offers more. It is possible, for example, to achieve acceptable resolution of the unre- solved Delta 2 diastereoisomers from the major manufacturing products (Delta 3 diastereoisomers) in the separation of the antibiotic Axetil E47 using an extremely efficient silica column. With a Hypercarb column, however, not only is base-line resolution achieved from the main pro- ducts, but separation of each isomer is realised, allowing total quantification. Shandon Scientific Ltd., Chadwick Road, Astmoor, Runcorn, Cheshire WA7 1PR. HPLC Column A new column has been designed specific- ally for carbamate pesticide analysis.The bonded-phase silica Carbamate Analysis Column separates 10 pesticide residues in accordance with EPA Methods 531 and 5 . Column dimensions are 150 x 4.6 mm internal diameter. The bonded substrate is 5 pm CIS silica. Each column is individu- ally tested and comes with its own chro- matogram of carbamate pesticides. Also available are hardware and reagents, which turn a standard HPLC system into a complete carbamate analyser. Pickering Laboratories, 1951 Colony Street, Suite S, Mountain View, CA 94043, USA. HPLC Detection of Pharmaceuticals The 750114 Evaporative Mass Analyser has recently been extensively used in the pharmaceuticals industry to analyse all components eluted from HPLC columns.The major application is in new drug impurity evaluation. Another application is in the analysis of raw materials (e.g., fish oils) for the pharmaceuticals industry. Gradient elution can also be used and the Mass Analyser is not temperature depen- dent. Applied Chromatography Systems Ltd., The Arsenal, Heapy Street, Mac- clesfield, Cheshire S K l l 7JB. HPLC Columns Accusphere columns are packed with custom-manufactured Accusphere silica in a choice of 3, 5 and 7 pm particle sizes. A selection of bonded functional groups such as octadecyl, octyl, methyl, cyano, amino, phenyl and diol provide a range of selectivities and pH stabilities.The col- umns are designed to handle the complete range of reversed-phase HPLC analyses, including organics, inorganics, proteins, amino acids, pharmaceuticals, alcohols, ions, carbohydrates, phenols, esters, pes- ticides and other compounds. J. and W. Scientific, 91 Blue Ravine Road, Folsom, CA 95630, USA. Immunoaffinity Kit The Affi-Gel Hz immunoaffinity kit offers high antigen binding capacity, as antibodies are coupled to the support only by their Fc regions. Hydrazide activated agarose beads are used to couple I,G molecules via carbohydrate moieties located on the Fc region of the antibody. Affi-Gel Hz exhibits 300% higher binding capacity for imrnobilised anti-BSA 1,G over CNBr-activated Sepharose I,G, and 100% higher capacity for immobilised anti-(3 galactosidase 1,G.The kit includes Affi-Gel Hz hydrazide gel, oxidiser, sodium periodate, coupling buffer con- centrate, Econo-Pac 10DG de-salting col- umns and an econo-column. Scale-up amounts of gel, oxidiser and buffer are available for preparative immunoaffinity purification.38 ANALYTICAL PROCEEDINGS, JANUARY 1989, VOL 26 Bio-Rad Laboratories Ltd., Caxton Way, Watford Business Park, Watford, Hertfordshire WD1 8RP. DNA Labelling Kit For the synthesis of DNA probes with a high specific activity a Random Primer DNA Labelling Kit has been introduced. Based on a method described by Feinberg and Vogelstein (Anal. Biochem., 1983, 132, 6), the kit enables the user to generate DNA fragments radiolabelled to a high specific activity (>1 X 109 cpm pg-I). Only a small amount of template (<200 ng) is required, and very short probes can be labelled.The probe can be used without removal of unincorporated nucleotides, while the DNA can be labelled in low gel temperature agarose with either isotope or biotin. More than 50% of the label is incorporated. Bio-Rad Laboratories Ltd., Caxton Way, Watford Business Park, Watford, Hertfordshire WD1 8RP. Microplate Reader The Model 3550 is a high-performance microplate reader that can accommodate changing priorities and assay require- ments. It features single or dual wavelength readings, taking only 12 or 22 s, respectively, to read an entire plate, including a 2-s calibration before each reading to eliminate drift. Software auto- matically analyses the data and receives commands entered through a comprehen- sive membrane keypad.Analysis proto- cols for plate reading and data processing can be specified and saved in the memory, including parameters such as reading mode (single or dual), interference filter selection, format number, printing options and plate mixing. The Kinetic ELISA function allows fast reading times, and an on-board plate mixer dispenses the reaction product evenly to ensure repro- ducibility. Plates may be read up to 23 times at specified time intervals. The Model 3550 can. be operated under com- puter control, and there is an optional automatic plate loader. Bio-Rad Laboratories Ltd., Caxton Way, Watford Business Park, Watford, Hertfordshire WD1 8RP. Fraction Collector The Model 2110 fraction collector offers cold-room compatibility and comes com- plete with an 80-tube carousel, a carousel dust cover and tubing connectors.A micro-tube adaptor fits into the standard tube carousel to convert it for use with 1.5 ml micro tubes. An optional accessory cable permits remote control and the output of event mark and conformation signals. Other features include time and drop collection modes, solvent resistance, a spill drainage system, sealed working parts and a two-tier carousel for easy removal. Bio-Rad Laboratories Ltd., Caxton Way, Watford Business Park, Watford, Hertfordshire WD1 8RP. Column for Direct Injection of Biological Fluids The Hisep shielded hydrophobic phase column for separating drugs, drug metab- olites, etc., from biological fluids, which are directly injected on to an analytical column, is designed to separate small compounds from protein containing Sam- ples without denaturing or precipitating proteins on the chromatographic support.Hisep columns demonstrate a high degree of physical stability and chromatographic reproducibility even after many samples have been injected. Many drugs can be separated with good recovery after spik- ing in human plasma or serum at thera- peutic levels. Supelco Inc., Supelco Park, Bellefonte, PA 16823-0048, USA. Packings Toyopearl resin based packings, formerly offered under the name Fractogel, are widely used for purifying and separating biopolymers and other biochemicals. Toyopearl resin is an ideal material for gel filtration, ion exchange, hydrophobic interaction and affinity chromatography. It resists acids, bases, organic solvents and microbial attack.Supelco Inc., Supelco Park, Bellefonte, PA 16823-0048, USA. Semi-dry Electrophoretic Transfer The makers’ family of blotting cells has been extended by the introduction of the Trans-Blot SD semi-dry electrophoretic transfer cell and the Trans-Blot plate electrodes. With applications in protein blotting, the Trans-Blot system offers fast, efficient transfers. Only 200 ml of buffer are required for blotting even a large gel. Times vary from 15-30 min for a mini-gel to 45-60 min for a large gel. The electrode surface area can accommodate gels ranging from a 20 cm Protean I1 gel to a 15 x 25 cm Subcell gel. Bio-Rad Laboratories Ltd., Caxton Way, Watford Business Park, Watford, Hertfordshire WD1 8RP. Endotoxin Removal Solutions intended for in vivo applications can now be rendered virtually endotoxin- free by means of Affi-Prep polymyxin support.Affi-Prep polymyxin support can withstand sanitisation with 1 N sodium hydroxide solution yet retain its affinity: 99.9% of applied endotoxins are bound even after an alkali wash. Affi-Prep poly- myxin support also resists 70% ethanol and 100% propan-2-01. Linear flow-rates up to 2000 cm h-1 are possible. The support is effective for the removal of endotoxin molecules from different ori- gins, such as strains of E. coli, Salmonella and Serratia. Bio-Rad Laboratories Ltd., Caxton Way, Watford Business Park, Watford, Hertfordshire WD1 8RP. DNA Electrophoresis The CHEF-DR I1 system has been spe- cially designed for the gel electrophoresis and resolution of megabase DNA mol- ecules.For use in a variety of molecular biology applications, including chromo- some arrangements, rflps, insert sizing, gene mapping and library screening, the CHEF-DR I1 (dynamically regulated clamped homologous electric field) com- bines electronic and electrophoresis tech- nologies to give straight lanes and the widest range of size separation of all pulsed-field techniques with enhanced resolution. Reproducible results and flex- ibility as regards sample type are possible, and the large gel format allows up to 30 lanes to be run. Over 12 million bases have been resolved by CHEF technology, although no upper limit has been esta- blished. Enhanced resolution is obtained in the 2000 to 1000000 base range and fragments as small as 222 bases have been separated.The system’s ability to sepa- rate 15 yeast chromosomes demonstrates its resolving capacity. Bio-Rad Laboratories Ltd., Caxton Way, Watford Business Park, Watford, Hertfordshire WD1 8RP. Mercury Electrode for HPLC Detection The Model 420 Mercury LC Electrode adds mercury reductive detection capabil- ity to the makers’ Model 400 electrochem- ical detector. It allows the detection of a wide range of electrochemically reducible compounds including organics, organ- ometallics, peroxides and ions. The Model 420 is a renewable mercury elec- trode detection system compatible with virtually any other electrochemical detec- tor on the market. EG&G Instruments, Doncastle House, Doncastle Road, Bracknell, Berkshire RG12 4PG.Differential Amplifier Non-aqueous titrations, particularly those in non-polar solvents with low conductivity, are susceptible to severeANALYTICAL PROCEEDINGS, JANUARY 1989, VOL 26 39 interference owing to static charges. The 6.2129.000 differential amplifier from Metrohm allows the recording of critical, non-aqueous titration curves free from interference on titrators without a built-in differential amplifier. It is compatible with all electrode sockets which conform to DIN 19 252. V. A. Howe and Co. Ltd., 12-14 St. Ann’s Crescent, London SW18 2LS. Karl Fischer Titration System The DTS830 titration system is a semi- automatic laboratory set-up for determin- ing water content in a vast range of food and other natural substances. Micro- processor controlled, it is equipped with a sample station which fully protects the Kadiometer V I 3 UJU Karl kischer titration system sample from atmospheric humidity.The station includes a waste pump, seven- speed magnetic stirrer and double plati- num electrode. A special container is supplied for the introduction of solid samples into the titration vessel. Radiometer Ltd., The Manor, Manor Royal, Crawley, West Sussex RHlO 2PY. Automated Karl Fischer System With the 678 EP/KF Processor, Metrohm have developed a new end-point and Karl Fischer titrator. Its strength is that, together with the 665 Dosimat, it allows the performance of automatic Karl Fischer moisture determinations with an extensive series of samples. Because it also offers the possibility of conducting general potentiometric end-point titra- tions (p and m values, Kjeldahl, etc.) as well as investigations of reaction kinetics, it is a universal end-point and pH-stat titrator.It is designed for KF titrations in 3 modes: titrations of individual samples, titrations with sample changer and with robots. V. A. Howe and Co. Ltd., 12-14 St. Ann’s Crescent, London SW18 2LS. Micropla t es Designed for use on all makes and types of automatic and semi-automatic micro- plate instrumentation, including the mak- ers’ Multiskan range, EIA I1 microplates offer new levels of binding characteristics and optical quality. The coefficient of variation is less than 5% across the whole spectrum and less than 2.3% in terms of optical clarity. Free samples are offered to users. Flow Laboratories Ltd., Woodcock Hill, Harefield Road, Rickmansworth, Hertfordshire WD3 1PQ.Conductivity Meters The CMD630 and CMD650 are designed for professional applications and have large digital displays. They offer high levels of accuracy, reliability and repeatability. Among their features are automatic and manual temperature com- pensation, multi-range facilities, and vari- able cell constant and temperature coeffi- cient. WPA Ltd., The Old Station, Linton, Cambridge CB1 6NW. Robot Arm for Laboratory Workstation A separate robot arm is now available for the makers’ Biomek 1000 laboratory workstation. The Biomek system auto- mates microtitre plate procedures, and the new robot provides walk-away auto- mation for microplate assays. Controlled through the workstation PC for the two units to operate in unison as part of a complete system, the robot is capable of exchanging all labware on the work- station, including disposable pipette tips, plates, tube racks and reagent reservoirs. It sits at the centre of a segmented circular table where labware is stacked in sets.Beckman, Progress Road, Sands Indus- trial Estate, High Wycombe, Bucking- hamshire. Biomass Determination Quick and convenient determinations of biomass can be made with the new Shimadzu TOC-500, which uses new com- bustion techniques giving carbon recovery rates close to 100%. Results for total organic carbon are available within 2 min, and these can be easily converted into biomass. An automated sample injector is available for use with the Dyson Instruments Ltd., Hetton Lyons Industrial Estate, Hetton, Houghton le Spring, Tyne and Wear DH5 ORH.TOC-500. Interfacing with LIMS IDAS (Instrument Data Acquisition System), a simplified, systematic approach to interfacing analogue, digital and intelligent laboratory instruments with the CALS Lab Manager LIMS, consists of the makers’ MK5 digital instru- ment coupler, LIL (Laboratory Interface Language) and LIL application pro- grams. It provides enhanced automated instrument control and real-time interac- tion with the host computer, while mini- mising the need for custom programming. It may be installed and operated in parallel with existing CALS data acquisi- tion subsystems (ADAS and EDAS) and existing user written data acquisition pro- grams. Beckman, Progress Road, Sands Indus- trial Estate, High Wycombe, Bucking- hamshire.Balance The PM series of electronic balances has been complemented by the addition of the PM1200 model, which provides a read- ability of 1 mg over its entire 1200 g weighing range. It embodies all construc- tive features of balances with the makers’ M-Technology and it has the DeltaTrac graphic display as well as the digital display. A vibration adaptor permits balance adaptation to various ambient conditions and a weighing process adap- tor permits adaptation of the display to the environment or to the object to be weighed. Mettler Instrumente AG, CH-8606 Greifensee, Switzerland. Software for Weighing The MultiRange ID5 control terminal now has available the SUMPAC applica- tions software, which provides greater clarity in the weighing records.Weighings of samples of the same type are recorded in partial quantities and summed to article totals for each article. The individual article totals are transferred to a customer total memory, which then calculates the delivery or customer total in shipment weighing and batching. In an indepen- dent operation, all weighing of partial quantities are summed for each article in the grand total memory. These are avail- able as a total record at the end of a specified time period or for the comple- tion of a consignment comprising several customer totals (e.g., truckload). Mettler Instrumente AG, CH-8606 Greifensee, Switzerland.ANALYTICAL PROCEEDINGS, JANUARY 1989, VOL 26 Lasers The Quantronix 4000 series lasers are optically-pumped, solid-state systems, which, in their basic versions, generate CW outputs at 1064, 1319 and 1053 nm.Options allow outputs at other wavelengths. Pulsed operation can be mode-locked or combined mode-locked/ Q-switched simply by selecting the appropriate intercavity modulation tech- niques. The 4000 series offers both Nd- YAG and Nd-YLF types. Lambda Photometrics Ltd., Lambda House, Batford Mill, Harpenden, Hert- fordshire AL5 5BZ. Literature A brochure outlines many ways in which advanced mass spectrometry can be used for quality control and a variety of appli- cations within the semiconductor industry. Two instruments are referred to: the VG PlasmaQuad inductively cou- pled plasma mass spectrometer and the VG9000 glow source mass spectrometer. VG Elemental Ltd., Ion Path, Road Three, Winsford, Cheshire CW7 3BX.A 50-page chromatography accessories catalogue contains details of hardware for chromatography. Among the items included are retrofit injector systems, outlet splitter systems, gas purifiers and filters, micro-needle valves and mass spectrometer interfaces, plus a wide range of tubing and fittings. It also includes the Pyrolysis system,' Univap gas sampling device, a multi-dimensional chromato- graphy accessory and a trace residue extraction system. Scientific Glass Engineering (UK) Ltd., Potters Lane, Kiln Farm, Milton Keynes MKll 3LA. A set of applications show the analysis of optically active sugars in complex mix- tures such as fruit juices and beers. Using the ChiraMonitor, the D- and L-sugars in regular and low calorie drinks are shown.The ChiraMonitor can detect whether a juice is chemically or naturally produced. Applied Chromatography Systems Ltd., The Arsenal, Heapy Street, Mac- clesfield, Cheshire SKll 7JB. A comprehensive market survey of the UK HPLC market is available. It contains 46 pages of detailed information about who leads the market place in HPLC instruments, consumables and access- ories. Market shares and sizes are detailed. HPLC Market Resources, Finlay Robertson, 5th Floor, Brook House, 77 Fountain Street, Manchester M2 2EE. A leaflet gives information on an auto- mated developing chamber for thin-layer chromatography. The chamber, which employs a double beam optical sensor for the detection of the solvent front, makes available a tool to perform chromato- graphy under identical conditions to those of manual methods. It is suitable for 20 x 20, 20 x 10 and 10 x 10 cm plates. bridge CB4 1TH. Camlab Ltd., Nuffield Road, Cam- A brochure describes a range of auto- matic titration systems for pH, redox, acid - base, dead-stop and argentimetric titrations, colorimetric end-points and Karl Fischer determinations. Camlab Ltd., Nuffield Road, Cam- bridge CB4 1TH. An applications publication explains how the Biomek 1000 automated laboratory workstation can be used to automate DNA sequencing according to the dideoxy method of Sanger and Coubon. Full details are provided on the methodol- ogy, which has been developed by Beck- man, including pipetting patterns used for template isolation in a 96-well plate. Beckman, Progress Road, Sands Indus- trial Estate, High Wycombe, Bucking- hamshire. A 64-page book describes the Physik Instrumente range of electro-optical benchware and accessories. Included are details of a vast range of optical com- ponents and equipment, from optical benches plus all relevant components to complete, fit-together, building block systems for numerous optical and electro- optical arrangements, including interfer- ometry, holography and fibre optic work. Lambda Photometrics Ltd., Lambda House, Batford Mill, Harpenden, Hert- fordshire AL5 5BZ.

ISSN:0144-557X    

DOI:10.1039/AP9892600037

出版商:RSC    

年代:1989

数据来源: RSC

摘要:

40 ANALYTICAL PROCEEDINGS, JANUARY 1989, VOL 26 Conferences and Meetings The Effects of Small Doses of Radiation February 7-8, 1989, London The biological effects of large doses of radiation have been known and under- stood for many years, but the elucidation of the effects of small doses has been much more difficult and controversial. This conference, which will be held in the Cafe Royal, sets out the main sources of information on the most important effect of radiation, the induction of cancer. After an indication of the principal sources of radiation to which man is exposed, internationally recognised experts will summarise the main studies that have led to our present understand- ing of the carcinogenic effect of small doses of radiation. The talks will be authoritative and will be aimed at an audience that is not expected to have any detailed biological training or experience.The intention will be to provide an easily understood account of the present state of knowledge in this difficult area. There will be ample opportunity for questions and discussion. The Conference will be of value to those in industry, medicine and govern- ment with an interest in the control of exposures of radiation. It will also provide a useful basis of comparison for those concerned with the effects of chemical carcinogens in the workplace and the environment. For further details, please contact: Katie Lye, IBC Technical Services Ltd., Bath House (3rd Floor), 56 Holborn Viaduct, London EClA 2EX. UK Instrumentation Series 1989 The remaining exhibitions in this series in 1989 will be held as follows: February 22-23, 1989, in the Harrogate Exhibition Centre; March 21-22, 1989, in the Crest Hotel, Filton, Bristol; and June 14-15, 1989, The Forum, Livingston.For further information contact Trident International Exhibitions Ltd., 21 Plymouth Road, Tavistock, Devon PL19 8AU. Pittsburgh Conference and Exposition on Analytical Chemistry and Applied Spec- troscopy March 6-10, 1989, Atlanta, GA, USA The 1989 conference and exposition will be held in the Georgia World Congress Center. Most branches of analytical chemistry and spectroscopy will be covered by the various sessions of the conference. For details write to the Pittsburgh Conference and Exposition on Analytical Chemistry and Applied Spectroscopy, 12 Federal Drive, Suite 322, Pittsburgh, Pennsylvania 15235, USA.ANALYTICAL PROCEEDINGS.JANUARY 1989, VOL 26 41 Document Image Processing March 14-16, 1989, London A conference on this subject will be held in the Queen Elizabeth The Second Con- ference Centre. For information contact Blenheim Online, Blenheim House, Ash Hill Drive, Pinner, Middlesex HA5 2AE. Occupational Safety and Health-Indica- tors of Management Quality. Dangerous Substances May 9-11, 1989, Mainz, FRG The topics of these conferences will be as follows. In the first part, “The Specific Responsibilities of Entrepreneurs and Management”; “The Organisation of Occupational Safety-Various Models and Experiences in Large, Medium-sized and Small Companies”; “Proposals and Suggestions for Entrepreneurs and Management”: and in the second part, “Cutting Coolants”; “Welding Fumes”; “Substitutes for Dangerous Substances”; “Preventive Medical Measures.” Various technical visits are also planned.For further information contact the Secretariat, Arbeitsgemeinschaft der Eisen- und Metall-Berufsgenossenschaf- ten, Kreuzstrasse 45, D-4000 Dusseldorf 1, Federal Republic of Germany. ChemAsia 89, InstrumentAsia 89 and AnaLabAsia 89 May 23-26, 1989, Singapore These three exhibitions will be organised by Singapore Exhibition Service Ltd. and held in the World Trade Centre, Singa- pore. Financial subsidies are available to British companies. For details of British participation contact Andrew Furness, Overseas Exhibition Services Ltd., 11 Manchester Square, London W1M 5AB. Sensors and Systems ’89 October 24-26, 1984, London Over the past years the Test and Trans- ducer Conference has become one of the more important international events in the measurement and sensors field.In 1989, with its associated Exhibition, it becomes Sensors and Systems ’89 and will be held at the Wembley Conference Centre. Papers should be of a non-com- mercial nature and of a high technical standard. The content of sessions will include overview, research and develop- ment and applications papers. Also, where it is possible, each session will include “hand on” experience for del- egates. Papers are invited describing ap- plications of advanced techniques and developments in any type of sensor, transducer or associated system. Authors should describe new instrumentation and techniques, involv- ing mechanical, electronic, optical and other methods used to effect measure- ments. Authors wishing to present papers should submit a synopsis (up to 500 words) on the attached form, together with brief autobiographical details as soon as possible. The closing date for the submission of offers of papers is January, 31, 1989. Notification of acceptance of papers will be made by April, 1989, and authors will be expected to submit com- pleted papers no later than July, 1989. Papers will be published in the bound volumes of the conference proceedings and speakers will receive complimentary copies. Please send all submissions to Norma Thewlis, The Conference Secretary, Trident International Exhibitons Ltd., 21 Plymouth Road, Tavistock, Devon PL19 8AU.

ISSN:0144-557X    

DOI:10.1039/AP9892600040

出版商:RSC    

年代:1989

数据来源: RSC

摘要:

ANALYTICAL PROCEEDINGS. JANUARY 1989, VOL 26 41 Courses Statistical Analysis of Laboratory Data March 6-10, 1989, Amsterdam, The Netherlands This course, which includes personal com- puter applications, is intended for labora- tory and plant support staff in the chem- ical process and health care industries. For information on the course contact The Centre for Professional Advance- ment, Palestrinastraat 1, 1071 LC Amsterdam. The Netherlands. Royal Society of Chemistry Continuing Education Programme 1989 The courses in this programme will be as follows. March 21-23, “Spectroscopy and Chromatography by Open Learning” at Thames Polyetechnic; March 28-31, “Computer Methods in Ultraviolet, Visible and Infrared Spectroscopy” at The Polytechnic of Wales; April 17-21, “High Resolution NMR Spectroscopy” at the University of Sheffield; July 10-13, “Application of Modern Chromato- graphic Techniques” at Thames Poly- technic; July 24-26, “Polymorphs and Solvates of Drugs“ at Bradford Univer- sity; September 3-8, “Medicinal Chem- istry” at the University of Kent; and September 18-22, “Molecular Biology and Biotechnology” at Hatfield Poly- technic.Further details are available from Ms. L. Hart, Royal Society of Chemistry, 30 Russell Square, London WClB SDT. European Spring School in Chemometrics April 2-7, 1989, Bristol Following the 1987 and 1988 European Spring School in Chemometrics, the Uni- versity of Bristol announces the 3rd European Spring School in Chemo- metrics (3rd ESpriSC), which will be jointly organised by the School of Chem- istry and Department of Extra-Mural studies.The course will be taught by an interna- tionally recognised team of tutors, from The University of Bristol (UK), The Free University of Brussels (Belgium), The University of Bergen (Norway), Glaxo Research, Co. Durham (UK), BP Research, Sunbury-on-Thames (UK), Janssen Pharmaceutica, Beerse (Bel- gium) and AFRC Food Research Insti- tute, Bristol (UK). Following and improving on the successful 1988 format the tutors will include a mixture of research-active chemists and statisticans, industrialists and academics. The course will aim to show chemists what software tools are available to improve the per- formance of and analyse laboratory instrumental data. Special features will include: extensive course notes, which will eventually form the basis of interna- tionally published texts and papers; extensive opportunities for hands-on use of software packages, many of which have been developed by course tutors and their colleagues; and collaboration with the EEC funded COMETT scheme for con- tinuing education.There will be a mixture of theoretical and applied tutorials, and most material will be divided into “Simple” and “Advanced” options to suit delegates’ prior experience. The academic course organiser is Dr. R. G. Brereton of the School of Chemistry, University of Bristol. The COMETT scheme is co-ordinated by Professor D. L. Massart of the Free University of Brussels. For enquiries please write to Dr. S. M. Pringle of the Department of Extra-Mural Studies, Wills Memorial Building, Queen’s Road, Bristol BS8 1HR.The course fee will be fully inclusive of all tutorials, meals, accommodation, social programme, notes, and internal transport. Accommo- dation has been improved since 1988, but because of the need to house delegates and tutors in a geographically compact area, in order to stimulate discussion and the flow of ideas throughout the course, better rooms will be allocated to delegates on a first-come first-served basis.42 ANALYTICAL PROCEEDINGS, JANUARY 1989, VOL 26 KINETICS IN ANALYTICAL CHEMISTRY The third in this series of international symposia will be held in Cavtat, near Dubrovnik, Yugoslavia, on September 25-28, 1989. The organisers will be The Serbian Chemical Society. The scientific programme, which will take place in the Croatia Hotel, will consist of plenary, invited and contributed papers and posters.The subject matter will include catalytic (enzymatic or non-enzymatic) and non-catalytic methods, differential reaction rate methods and unsegmented flow methods. The scientific committee is as follows: Professor H. A. Mottola (Stillwater, Oklahoma, USA); Professor G. Werner (Leipzig, GDR); Professor M. Valcarcel (Cordoba, Spain); Professor M. I. Karayannis (loannina, Greece); Professor G. A. Milovanovic (Belgrade, Yugoslavia); and Professor F. F. Gaal (Novi Sad, Yugoslavia). For further information concerning the conference contact Professor Gordana A. Milovanovic, Department of Chemistry, University of Belgrade, KAC, P.O. Box 550, 11001 Belgrade, Yugoslavia. Call for Papers 1990 Winter Conference on Plasma Spectrochemistry January 8-13, 1990, St.Petersburg, Florida, USA The 1990 Winter Conference on Plasma Spectrochemistry will be held from Monday, January 8 through to Saturday, January 13, 1990 in St. Petersburg, Florida at the St. Petersburg Hilton and Towers. The 1990 Winter Conference, sixth in a series of biennial meetings sponsored by ICP lnformation Newsletter, will feature developments in plasma spectrochemical analysis by inductively coupled plasma (ICP), d.c. plasma (DCP), microwave induced plasma (MIP) and glow and hollow-cathode discharge (GDL, HCL) sources. Professional short courses will be presented on Saturday and Sunday, January 6 and 7, and Saturday, January 13, and a three-day exhibition of spectroscopic instrumentation and accessories will also be included. Symposium topics will include: (a) chemometrics in plasma spectroscopy; (b) chromatography with plasma source detection; (c) ICP mass spectrometry and interferometry; (d) instrumentation automation and robotics; (e) low-pressure discharges; (0 mechanisms and processes in plasma sources; (9) new plasma spectroscopy instrumentation; ( h ) process control, remote and on-line plasma analysis; ( i ) sample introduction techniques and phenomena; ( j ) sample preparation and calibration techniques; and ( k ) spectrochemical applications of plasmas. Titles and 50-word abstracts for submitted papers are solicited by July 3, 1989. For further information, write to: 1990 Winter Conference on Plasma Spectrochemistry, ICP lnformation Newsletter, Department of Chemistry, GRC Towers, University of Massachusetts, Amherst, MA 01 003-0035, USA, attention Dr. Ramon Barnes, or telephone (41 3)-545-2294.

ISSN:0144-557X    

DOI:10.1039/AP9892600041

出版商:RSC    

年代:1989

数据来源: RSC

摘要:

ANALYTICAL PROCEEDINGS, JANUARY 1989, VOL 26 43 Analytical Division Diary JANUARY Wednesday, 25th, 4 p.m.: Belfast Northern Ireland Region Retention and Selectivity in Supercritical Fluid Chromato- Speaker: R. M. Smith. Room 1078, Chemistry Department, Queen’s University, There are no registration formalities. Contact: Mr. W. J. Swindall, Department of Chemistry, David Keir Building, Queen’s University, Belfast BT9 5AG. (Tel. 0232-661111, Ex. 4428). graphy * Belfast. Thursday, 26th: Manchester and Liverpool North West Region. Analysis and Crime. Schools Lecturer: R. L. Williams. UMIST, Manchester, and Liverpool. Registration is necessary. Contact: Mr. G. Davison, 34 Beechfields, Doctors Lane, Eccleston, Chorley, Lancashire PR7 5RE. (Tel. 0257- 452537). Friday, 27th: Macclesfield and Carlisle North West Region.Analysis and Crime. Schools Lecturer: R. L. Williams. Macclesfield and Carlisle. Registration is necessary. Contact: Mr. G. Davison, 34 Beechfields, Doctors Lane, Eccleston. Chorley, Lancashire PR7 5RE. (Tel. 0257- 452537). FEBRUARY Wednesday, lst, 10 a.m.: London Chromatography and Electrophoresis Group, jointly with Multi-dimensional Techniques in Chromatography. ”Multi-dimensional Gas Chromatography-New Aspects and “Column Switching in Liquid Chromatography.’’ by C. Little. “Thin-layer Chromatography - Mass Spectrometry.” by D. Hill- “LC - LC Methods Applied to Sample Clean-up,“ by T. Chilton. “Multi-dimensional LC - LC and LC - GC in the Trace Analysis of Food,‘’ by M. Shepherd. Scientific Societies’ Lecture Theatre, New Burlington Place.off Savile Row, London W. 1. Registration is necessary. Cost to RSCiCS members f35, and non-members f50. Contact: Dr. D. Simpson, Analysis For Industry, Factories 213, Bosworth House, High Street, Thorpe-le-Soken, Essex C016 OEA. (Tel. 0255-861714). the Chromatographic Society. Latest Techniques,” by A. C. Heim. beck. Drug Abuse in Sport. Speaker: D. Cowan. Lecture Theatre J0Ol , Edward Herbert Building, University of Technology, Loughborough. There are no registration formalities. Contact: Mr. H. E. Brookes, 35 Dunster Road, West Bridgford, Nottingham NG2 6JE. (Tel: 0602-231769). Wednesday and Thursday, 8th and 9th: London Analytical Division. F!ow Analysis Methods. Wednesday, 8th- “New Approaches to Detection in Flow Injection Analysis “Minireactor Columns in Flow Systems,” by A.Townshend. “Clinical Applications of FIA,” by B. Rocks. “Spectroscopy’s Answer to the Nernst Equation,” by J . F. Tyson. “Flow Injection Analysis with Amperometric Detection,” by A. G. Thursday, 9th- “FIA Systems using Antibodies and other Receptor Proteins,” by J . N. Miller. “Improvements in Biosensor Performance Through the Application of Flow Methods.“ by M. J . Eddowes. “Programmable FIA-A Step Closer to Industry,” by P. R. Fielden. “Solvent Extraction,” by M. Harriott. “Flow-injection Applications of Microemulsions,” by P. J . Wors- fold. Scientific Societies’ Lecture Theatre, 23 Savile Row (entrance in New Burlington Place), London W.l. Registration is necessary. Cost for two-day registration is &42 for RSC members, 275 for non-members and €20 for students and retired members; one-day registration is f26 for RSC members, 250 for non-members and f12 for student and retired members.Contact: Miss P. E. Hutchinson, Analytical Division, Royal Society of Chemistry, Burlington House, Piccadilly, London W1V OBN. (Tel. 01-437-8656). Systems,” by M. Valcarcel. Fogg. Wednesday, 8th, 4.30 p.m.: Salford Students Chemical Society. North West Region, jointly with the Salford University The Education and Training of Analytical Chemists in the Developing Countries. It is anticipated that the meeting will be of interest to members and guests who are involved with the educational activities of the British Council in the developing countries. University and Polytechnic super- visors of students from abroad will also find the meeting of interest and they are invited to attend and contribute to the discussion.The meeting will open with a short presentation by L. S. Bark. Research Professor of Chemistry at the University of Salford, and continue with supporting speakers who have experience in this area of education. There are no registration formalities. University House, The University, Salford. Contact: Mr. E. D. Worthington, Bolton South Sixth Form College, Lever Edge Lane, Bolton BL3 3HH. [Tel. 0204-62524 or (home) 0706-214905]. Tuesday, 7th, 4.15 p.m.: Loughborough Midlands Region, jointly with the East Midlands Section of the RSC and Loughborough University Students Chem- ical Society. [conrinued on p . 44144 ANALYTICAL PROCEEDINGS, JANUARY 1989, VOI, 26 Analytical Division Diary, continued February, continued Thursday, 9th, 4.15 p.m.: Aberdeen Scottish Region, jointly with the Aberdeen and North of Scotland Section of the RSC and the Aberdeen Students Chemical Society.Quality Control of Analytical Results. Speaker: G. Topping. Department of Chemistry, University of Aberdeen, Meston There are no registration formalities. Contact: Mr. R. I. Aylott, United Distillers plc, Group Central Laboratory, Menstrie, Clackmannanshire F K l l 7ES. (Tel: 0259-61701). Walk, Old Aberdeen. Tuesday, 14th, 10 a.m.: Stevenage East Anglia Region and Chemometrics Group. An Introduction to Chemometric Methods. Introduction by Chairman. “Understanding Statistics,” by J. Mendham. “The Importance of Calibration,” by M.Thompson. “Optimisation and Experimental Design,” by S . J. Haswell. “Applications of Pattern Recognition,” by K. Burton. “ExploratoryiNon Parametric Methods,” by J . M. Thompson. “Software Validation,” by M. Adams. Warren Spring Laboratory, Gunnels Wood Road, Stevenage, Hertfordshire. Registration is necessary. Cost f35 to RSC members, f60 to non-members and 215 to students and retired members. Contact: Mr. P. R. Brawn, Unilever Research, Colworth Laboratory, Sharnbrook, Bedfordshire MK44 1LQ. (Tel. 0234-22201 1). Wednesday, 15th, 10.30 a.m.: Middlesbrough North East Region and Atomic Spectroscopy Group. Inductively Coupled Plasma Mass Spectrometry. Overseas Speaker, to be announced. Bioavailability and Speciation Studies Using ICP-MS,” by H. M. 6’Supply and Demand in ICP-MS,” by J.Marshall. “Applications of ICP-MS in the Nuclear Industry,” by R. M. Brown. ‘Clinical and Environmental Applications of ICP-MS,” by H. T. Hilger Spectroscopy Prize Winner 1988: “Sample Introduction ICI Wilton Centre, Wilton, Middlesbrough. Registration is necessary. The cost is f 1 5 for members of the RSC and f 3 5 for non-members; for full-time students and retired RSC members $7. Contact: Dr. J. R. Dean, Department of Chemical and Life Sciences, Newcastle upon Tyne Polytechnic, Ellison Terrace, Ellison Place, Newcastle upon Tyne NE1 8ST. (Tel. 091-232-6002). Crews. Delves. Techniques for ICP-MS,” by J . Williams. Wednesday, 15th, 6.30 p.m.: London South East Region, Micro & Chemical Methods and Chro- Chiral Separations. The speaker will emphasise the impor- tance of chiral separation, and describe how this can be achieved.matography & Electrophoresis Groups. Discussion to be introduced by D. Stevenson. Room A 506, London School of Economics, Houghton There are no registration formalities. Contact: Mr. P. R. W. Baker, 55 Braemar Gardens, West Street, London WC2. Wickham, Kent BR4 OJN. (Tel. 01-777-1225). Tuesday, 21st, 4.10 p.m.: Swansea Western Region: jointly with the South Wales West Section Science and Crime. Speaker: R. L Williams. Chemistry Department, University College, Swansea. There are no registration formalities. Contact: Mr. F. W. Sweeting, Wessex Water Authority, Regional Scientific Centre, Mead Lane, Saltford, Bristol BS18 3ER. (Tel. 0225-873692, Ex. 124). of the RSC. Wednesday, 22nd, 10 a.m.: London South East Region and Particle Characterisation Group.Measurement of Man-made Mineral Fibres. Welcome and Introduction by T. Ogden. “Overview of Man-made Mineral Fibres,” by J . N. Dawson. “Technical Performance and Occupational Hygiene Aspects of “Electron Microscope Measurement of Man-made Mineral Fibres ,” “Health Related Studies of Devitrified Refractory Ceramic Glass “Airborne Man-made Mineral Fibres from Loft Insulation,” by T. Discussion Forum by T. Ogden. Occupational Medicine and Hygiene Laboratory, Health and Safety Executive, 403/405 Edgware Road, London NW2 6LN. Registration is necessary. The cost is 215 for members of the RSC, 220 for non-members and f 5 for bona fide students and retired members. Contact: Dr. A. Rood, Occupational Medicine and Hygiene Laboratory, Health and Safety Executive, 4031405 Edg- ware Road, London NW2 6LN. (Tel. 01-450-8911). Ceramic Fibres Used by British Steel,” by G. Smith. by J . Cherry. Fibres,” by J. Young Jaffrey. Wednesday, 22nd, 10.45 a.m.: Didcot Radiochemical Methods Group. Environmental Radioactivity. “The Terrestrial Monitoring Programme (TRAMP) ,” by B. Walters. “Monitoring for Natural Radioactivity,” by J. C. H. M. Miles. “The Radiological Incident Monitoring Programme (RIMNET) ,” by “A CEGB View,” by A. Ware. “Environmental Monitoring Round the BNFL Sellafield Site,” by “Protection from Radionuclide Discharges,” by B. 0. Wade. Harwell Laboratory, Didcot, Oxfordshire. Registration is essential. Cost 220 for RSC members, f30 for non-members and f10 for senior citizens and students. Contact: Dr. J. S. Hislop, Chemical Analysis Group, Harwell Laboratory, Harwell, Didcot, Oxfordshire OX11 ORA. (Tel. 0235-24141). S. Newstead. E. Jones

ISSN:0144-557X    

DOI:10.1039/AP9892600043

出版商:RSC    

年代:1989

数据来源: RSC